Shotcrete and Guniting Air Supply

Reddy Compressors

Translate machine supplier requirements and site conditions into air duty. The required asset is the Concrete Spraying Air Requirement Brief.

The engineering conclusion is to specify usable air at the supplier-defined interface during the agreed operating scenarios. A compressor label, a static gauge reading or a concrete output figure alone does not define the air duty.

Document navigation

Part A contains the engineering article, sections 1 to 60. Part B contains the required reusable brief, sections 61 to 66. Use Word heading navigation to reach each numbered section.

Part A Engineering article

1 Purpose and direct answer

Shotcrete and guniting air supply should be specified from the spraying equipment supplier’s requirements, then checked against the installed route and the site operating plan. Record the required flow with its reference conditions, the required pressure at a named connection while air is flowing, the permitted upper pressure, and the process conditions to which those requirements apply. Assess the complete supply path against that record.

The useful procurement output is a duty brief. It identifies what is known, which values remain unconfirmed, who will confirm them, and how delivery will be demonstrated. A completed enquiry is distinct from an approved equipment selection. An air-duty acceptance is also distinct from acceptance of the sprayed concrete.

2 What shotcrete and guniting mean here

Shotcrete describes sprayed concrete or mortar and includes wet-mix and dry-mix processes. The American Shotcrete Association uses Gunite for the dry-mix process: material travels pneumatically to the nozzle and water is introduced there. In the conventional wet-mix arrangement, a prepared mix is pumped to the nozzle, where compressed air accelerates it. Preserve the supplier’s exact process description in an enquiry; do not infer the transport mechanism solely from a site nickname.

It does not treat every material described commercially as gunite, refractory gunning or sprayed mortar as interchangeable. A change of material or machine must reopen the relevant requirement fields. No air requirement should be transferred to another process merely because the name is similar.

3 The machine and process boundary

Identify three separate paths: compressed air from the source to the specified air connection; material from the feeding or pumping equipment to the nozzle; and water or admixture services where applicable. Record where these paths meet. A change in the material delivery hose does not automatically create the same loss in the air hose, even when both follow the same route.

The machine supplier defines the required air envelope and the limits of the machine/nozzle configuration. The air supplier demonstrates delivery capability at the agreed boundary. The spraying contractor and project engineer retain responsibility for process settings, material suitability, placement and concrete acceptance. Name the owner of each boundary before commissioning and retain the relevant supplier or project requirement.

4 The wet process air interface

For the conventional pumped wet-mix arrangement, the air enquiry must refer to the installed nozzle or spraying assembly and its intended operating range. Pump output identifies a material operating condition; it is not an air consumption rating. A nozzle substitution can invalidate an earlier air selection even if the pump is unchanged. The ASA technical note identifies nozzle design and air delivery restrictions as influences on wet-mix performance.

Ask whether the supplier’s air statement applies at the compressor, machine inlet, boom connection or nozzle manifold. If a machine-inlet requirement already includes internal distribution, do not add those internal losses again. If only a nozzle requirement is available, the upstream machine air path remains to be defined. Record the distinction explicitly in the pressure budget.

5 The dry process air interface

For a dry-mix configuration using pneumatic material transport, request the supplier’s duty for the actual material, feed setting, delivery hose and lift. Air demand belongs to an operating combination; it cannot be transferred unchanged from another machine simply because both are described as dry-mix. Water addition and its own pressure or control requirements remain a separate service specification.

Document the manufacturer’s allowable combinations and restrictions before evaluating capacity. If the route lies outside the supported envelope, request supplier assessment or an approved trial. Do not invent a pressure increment per metre of material hose or a generic relation between material output and air flow. The enquiry must expose this information gap rather than hide it inside a margin.

6 Process distinctions that do not become universal sizing rules

Wet/dry terminology identifies where air acts, but does not establish that every dry process needs more air than every wet process. Mechanised spraying assemblies and hand nozzles can have very different duties. The ASA technical material discusses different nozzle arrangements, making configuration identification essential.

Use process names as enquiry fields and search terms. Select equipment from documented requirements for the named assembly. Where a supplier supports more than one process, identify the mode to which each air requirement applies.

7 The supplier evidence pack

Request the machine make, model, serial or build configuration, manual revision, nozzle designation, approved material delivery arrangement, air requirement curve or table, and operating restrictions. Obtain the distinction between minimum usable pressure, recommended operating range and maximum permitted inlet pressure. Mark whether a value represents a continuous requirement, a peak or a test condition.

Where a quotation says only “air required”, ask for the connection location, flow basis, simultaneous accessories included and site correction method. Preserve the original statement alongside the clarified value. An enquiry remains open when these facts are missing; filling the gaps with familiar industry figures conceals the uncertainty the brief is intended to resolve. Record the source page or table so another reviewer can reproduce the interpretation.

8 Recording the supply path

Use a connection schedule even where no drawing is supplied. A recording sequence might be compressor outlet, treatment inlet, treatment outlet, site header, branch take-off, final hose, machine inlet, then the supplier’s internal air circuit. Assign a tag to each measurement point. This sequence is a recording convention, not a mandatory treatment arrangement.

For every segment, name its supplier, bore, length, fittings, design limits and evidence source. Record branches that bypass treatment or join downstream. The schedule should identify which party owns a loss, leak, contamination point or unresolved connection without assuming that all equipment belongs to the compressor package. Preserve the as-installed arrangement with the test record.

9 Pressure and flow as a paired requirement

Pressure describes the delivery condition; flow describes how much air is delivered on its stated basis. A duty is incomplete if one is omitted or if they refer to different locations. Check available compressor delivery at the intended operating pressure using documented performance, rather than inferring it from engine or motor power.

A practical requirement reads: required reference flow at a stated minimum dynamic pressure at interface B for operating scenario X. Record the upper allowed pressure independently. A minimum-pressure calculation is not permission to exceed the upper limit during idle periods, regulator failure or control transitions. The supplier should clarify whether its nominal setting is a requirement, an example or a limit.

10 Static readings and dynamic evidence

A gauge reading taken with a shut valve cannot demonstrate delivery during spraying. Establish a measurement condition that matches the duty: the relevant machine, selected mode and permitted concurrent users operating together. Record a time series where short events or cycling matter. Keep the operating state and sensor location with every result.

A single low-pressure observation cannot identify the cause. It may reflect supply limitation, route loss, an uncontrolled additional demand, a measurement error or a machine condition. Compare simultaneous readings across named boundaries so the pressure differences describe the same event rather than unrelated moments. A later recovered pressure must not replace the recorded minimum during the required duty.

11 Flow units and reference conditions

Write the flow unit and its reference basis in every duty table. FAD, standard volume, normal volume and actual line volume must not be treated as identical merely because they are labelled m³/min or cfm. The Atlas Copco manual demonstrates reconciliation of reference temperature and pressure before requirements are added.

For a purely volumetric unit change on an unchanged basis, 1 m³/min is approximately 35.3147 ft³/min, and 1 m³/min is 16.6667 L/s. Unit conversion does not correct changed reference conditions. Retain the supplier’s original units and the normalized working values so reviewers can reconstruct the calculation. Do not silently assume what “standard” means in an unqualified quotation.

12 Absolute pressure and gas basis

For a dry ideal-gas screening calculation with the same mass flow, the volume rate at basis 2 equals the rate at basis 1 multiplied by absolute pressure 1 divided by absolute pressure 2, then multiplied by absolute temperature 2 divided by absolute temperature 1. If compressibility is relevant, include the ratio of compressibility factors, basis 2 divided by basis 1. Use kelvin and absolute pressure; gauge pressure is unsuitable for this conversion.

This is a gas-basis conversion, not a model-specific compressor correction. Humidity, meter conventions and supplier test methods may need additional treatment. Record assumptions and ask the supplier to confirm the common comparison basis. Do not use this calculation to claim that a compressor retains a particular capacity at altitude. Example 3 demonstrates why two reference-volume numbers cannot always be compared directly.

13 Building the pressure budget

Start from the supplier-defined dynamic requirement at the terminal boundary. Add upstream pressure differences at the scenario flow, using suitable manufacturer data or validated calculations. Identify the compressor control condition at which the endpoint must still meet its requirement. A budget based only on the highest discharge reading can conceal a shortfall in the lower part of a control cycle.

Keep losses in named rows: treatment, common header, branch, valves, fittings and final connection. A component’s allowable working pressure is not its flow resistance. Do not add an arbitrary percentage to conceal unknown components; retain unresolved rows until evidence is obtained. Example 1 demonstrates the arithmetic without supplying a universal design pressure.

14 Common headers and individual branches

A common header carries the combined demand of active downstream branches. Each branch carries its own demand. Evaluate the common segment for the simultaneous scenario, then follow each terminal route separately. The longest branch is not automatically the governing branch if another has a more restrictive connection or a higher terminal requirement.

Create a pressure path for every material operating scenario. For each path, record the terminal requirement and all included losses. Compare the source requirements while preserving each endpoint’s upper limit. A shared higher-pressure header may require separately designed regulation for another user; that decision needs component and control evidence. Do not sum parallel branch losses as though all air passes through every branch.

15 Hose bore length and connections

Record actual internal bore, assembled length, lining condition and the minimum passage through couplings and adaptors. Nominal connection names and outer hose diameters are insufficient for loss assessment. Atlas Copco’s distribution guidance identifies fittings and flexible connections as contributors to delivery loss; its general network recommendations should not be copied as universal shotcrete acceptance limits.

Use the selected hose and fitting suppliers’ flow data where available. A route survey should count reducers, elbows, tees, isolation valves and temporary extensions. If fitting data are unavailable, mark the uncertainty and plan measured verification. Avoid deriving a hose size from a compressor outlet thread alone or assuming two externally similar couplings have the same passage.

16 Compressible flow calculation boundaries

Evaluate a long air route using a method valid for its pressure ratio, temperature assumptions and component restrictions. A constant-density liquid calculation can be a poor representation where air density changes appreciably. A small restriction may dominate the route and can approach a limiting flow condition; raising upstream pressure does not create an unrestricted increase in usable flow.

Record the calculation method, input basis and applicable range. Do not present an unvalidated website calculator as a machine guarantee. Use calculations to identify candidate arrangements, then validate the installed configuration under the agreed scenario with appropriate measurements and supplier participation where required. Keep estimated and measured losses visibly distinct in the record.

17 Final hoses and machine internals

Inspect the complete path beyond the main header. A generously sized main cannot correct a small final hose, restrictive adaptor or unsuitable regulator. Conversely, a satisfactory machine-inlet reading does not establish nozzle pressure if the machine’s internal air circuit has changed or its loss was excluded from the requirement.

Record temporary test fittings and meters because they can alter the tested path. If a measurement arrangement is removed after acceptance, confirm that the final operational arrangement has no greater restriction. Keep the supplier’s approved internal settings separate from site adjustments; the air brief does not authorize modification of the spraying head.

18 Material route and elevation

Survey material hose length, bore, vertical rise, bends and route changes separately from air distribution. For pneumatic dry-mix delivery, these conditions belong to the supplier’s process-duty assessment; for conventional pumped wet-mix they also affect the material system delivering the intended nozzle condition. The ASA FAQ discusses route and concurrent operations, but its examples are not adopted here as universal ratings.

Do not apply a water-column rule to the compressed air line or treat a material-hose pressure requirement as air-hose friction loss. Send the actual route to the appropriate supplier and retain the approved operating envelope. If a route changes, identify which air and material assumptions require reassessment.

19 Ambient conditions and altitude

Record site elevation or ambient pressure, expected temperatures, cooling conditions and intended power source. Atlas Copco’s altitude guidance explains that inlet conditions, compressor type and drive system affect performance and recommends supplier-specific evaluation.

Ask the compressor supplier to state available delivery on the agreed reference basis at the required pressure and site conditions. Check treatment equipment at its own inlet conditions. A favourable compressor statement does not establish dryer capacity or cooling performance, and a sea-level catalogue figure is not site-duty confirmation. Separate ambient conditions from the chosen reference-volume basis.

20 Siting and environmental exposure

Put actual location constraints in the enquiry: service access, surrounding heat sources, airborne dust, weather exposure, cooling airflow, noise restrictions and the authority responsible for installation. These are information requirements, not a statement that a particular arrangement is acceptable. Exhaust, ventilation and work-area exposure require the project’s equipment and site procedures.

Record proposed relocations that lengthen the air route. A decision made for access or logistics can change delivery losses and the coldest exposed section. Show planned operating positions and the acceptance-test configuration on the route record. A successful test in one position does not automatically cover all later positions.

21 Operating scenarios and duty duration

List operating states explicitly: one spraying user, full permitted concurrency, startup, a permitted accessory joining, steady spraying, pauses and controlled shutdown. Specify the duration of demanding states and how often they repeat. Average shift consumption cannot demonstrate a continuous peak duty. A time-weighted average can inform energy assessment while still being inadequate for delivery assessment.

Distinguish an operating restriction from a casual intention. If two users are assumed never to run together, state how that is managed and who owns it. Where concurrency remains possible, evaluate it. A receiver may bridge a bounded transient but cannot supply a continuing deficit indefinitely. Keep the evidence for any sequence restriction with the scenario register.

22 Simultaneous users

Build a register covering spraying assemblies, approved blowpipes, pneumatic tools, controls and other loads sharing the source. Record each user’s documented flow and pressure, operating state, and whether its demand is already included in a machine package figure. The ASA FAQ discusses testing a blowpipe and spraying operation together when they share air.

Add demands only on a common basis and at the correct boundary. Avoid a generic diversity factor or an assumed usage percentage multiplied by installed equipment count. A shared utility arrangement needs an agreed concurrency schedule and a test that challenges it. An accessory with low average use may still matter if it joins during the governing spraying scenario.

23 Demand accounting without double counting

Keep process users, treatment consumption, drains, measured leakage and separately justified future duty in different rows. Some package data are gross and others net of internal use. Obtain the definition before adding dryer purge or package control air. List uncertainty separately from demand; “unknown” is not zero, and an allowance must not be described as a measurement.

Total the required common-basis flows once for each scenario. Compare that total with usable supply at the matching boundary. If supply is measured downstream of treatment, do not subtract treatment use again. Every term must trace to a source, measurement or clearly labelled design assumption. Resolve whether intermittent treatment cycles overlap the governing user event.

24 Choosing a compressor from a documented duty

Give the supplier the combined flow, pressure path, site conditions, duty duration, quality requirements and connection schedule. Request confirmation of delivery at the relevant operating point, applicable control range, utilities and restrictions. Compare proposals against the same scenario, location and reference basis.

Treat maximum pressure and rated flow as separate claims until the supplier confirms they apply simultaneously. Avoid selection by power alone or borrowing a model’s best flow value from a lower-pressure setting. Where a proposal changes the operating arrangement, update the brief and assess the change explicitly. Keep supplier qualifications with the accepted proposal rather than removing them from the comparison.

25 Onboard and external air arrangements

Some mechanised spraying equipment is offered with an onboard compressor option. Putzmeister’s equipment information provides an example; it does not establish the configuration of the user’s machine. Verify the build specification and whether an external connection is approved for the intended mode.

For an onboard unit, identify included demands and whether external accessory use is permitted. For an external source, identify the connection and control responsibilities. Do not assume that onboard and external sources can be joined or run in parallel. Obtain the approved interface and source-selection procedure, and identify the measurement point that remains valid for each permitted mode.

26 Parallel sources and standby supply

A parallel-source proposal requires an engineered arrangement for pressure compatibility, isolation, reverse-flow prevention and control coordination. Two nameplate flows must not simply be added without confirming each source’s delivery at the common pressure and site conditions. Common treatment and header components must support the combined duty.

Standby capacity needs a separate recovery requirement. State whether a controlled process stop is acceptable, what happens before restart, and how the standby source becomes available. Do not describe manual standby as uninterrupted supply or claim N+1 coverage without demonstrating the defined duty and failure scenario. Preserve any limits on concurrent source operation in the handover.

27 Air quality at the interface

Ask the machine and process suppliers for permissible particulate, oil, liquid-water, vapour and temperature conditions at the actual inlet. Keep numerical requirements with their source and test method. “Clean dry air” should trigger clarification rather than an invented filtration class or dew-point number.

If a quality class is specified, record its edition, contaminant categories, location and sampling conditions. Do not infer a complete requirement from one filter grade. An oil-free compressor description alone does not describe every possible contaminant introduced downstream.

28 Moisture and the coldest route

Compressed air may carry water vapour and entrained liquid. Cooling downstream can produce liquid water even when the compressor outlet appears satisfactory. Atlas Copco’s moisture guidance describes moisture as a concern for systems and end products. Identify the coldest expected downstream condition and obtain a suitable supplier-approved moisture requirement.

Associate pressure dew point with its specification or measurement pressure. Do not directly compare an unlabelled atmospheric dew point with a line condition. Avoid claiming one fixed dew point is sufficient for every site. Example 5 illustrates the comparison while leaving the project’s acceptance requirement with its owner. Temperature history matters where a line passes between warm and exposed areas.

29 Aftercooling separation and drainage

An aftercooler, liquid separator and dryer perform different functions. Where included, record each unit’s inlet conditions, flow basis, outlet requirement, pressure loss and drain arrangement. Liquid separation alone does not establish water-vapour removal. Evaluate the complete path, including downstream exposure and collection points.

Include drain operation in commissioning and inspection. A drain that retains liquid and one that wastes air create different problems and need different evidence. Specify how condensate is collected and managed under the site arrangements without inventing environmental compliance claims. If a low point is inaccessible during operations, resolve its maintenance and drainage arrangement during design.

30 Dryers filters and operating basis

Select treatment from required inlet/outlet conditions and verified capacity data, not a matching connection size. Record relevant manufacturer correction factors and losses at the actual duty. Where loading changes filter pressure loss, use the agreed service condition and maintenance trigger rather than only a clean-element value.

A bypass changes the quality boundary and may change pressure loss. Identify permitted bypass modes and obtain the responsible machine/process owner’s approval before relying on them. Record replacement-element specifications and sampling locations so maintenance substitutions do not silently change the accepted arrangement. The air-quality decision and the pressure-budget decision must remain consistent.

31 Lubrication and branch segregation

Pneumatic accessories may have lubrication requirements different from process-air users. Record these individually and locate branch lubricators only within supplier-approved accessory branches. Confirm how return paths and shared hoses are controlled; a downstream non-return device alone does not establish overall contamination control.

A hose previously used for lubricated tools should not automatically be accepted for a different quality duty. Its reuse needs an owner-approved assessment or replacement. Retain hose identification, service history and quality boundary in the brief. Temporary cross-connections and borrowed site hoses should be visible changes, not undocumented conveniences.

32 Controls and operating limits

Define who may change source pressure, branch regulator and machine air settings. Record approved ranges and how the settings are identified. The machine supplier defines the response to loss or restoration of air and required interactions with material feed, water or additive systems.

Evaluate regulator or control-valve behaviour at demand, including droop or recovery relevant to the machine requirement. The displayed setpoint is not guaranteed outlet pressure. If a proposed adjustment affects more than one user, reassess each affected operating scenario and upper limit.

33 Isolation and depressurisation boundary

The commissioning plan must reference equipment and site procedures for isolation, stored energy and confirmation of depressurisation. Identify trapped sections between valves or non-return devices. Disconnection, clearing and repair remain activities for competent personnel under the applicable approved procedures.

This article supplies no air-blast blockage-clearing sequence or permission to raise pressure against an obstruction. For suspected blockage or abnormal material conditions, record the symptom and refer to the machine/process procedure. An air-capacity calculation does not authorize intervention. Retain the distinction between diagnostic observations and physical corrective actions.

34 Measurement architecture

Use named locations and time-aligned observations to separate source, treatment, distribution and machine behaviour. Record sensor range, calibration status, units, sampling interval, pressure reference and operating event. Flow meters must suit their pressure, temperature, flow basis and installation arrangement.

Agree the precision needed to resolve the acceptance limit before testing. If uncertainty overlaps the limit, report an inconclusive result rather than rounding to a pass. Keep raw observations with the interpretation. A manually copied “normal” reading cannot explain a brief collapse, and readings taken at different times cannot reliably establish the loss across a changing load.

35 Establishing a baseline

Before attributing a spraying problem to air supply, record machine setup, material condition, nozzle, route, active users and site conditions. Compare with the last accepted configuration. Capture a normal period and the complaint event where the approved procedure permits it.

A baseline includes source pressure and state, pressure at the duty interface, relevant treatment readings and the user sequence. Record recent maintenance and substitutions. The purpose is to identify the changed boundary, not to decide in advance that the compressor or process is responsible. Preserve the operator’s symptom description separately from the technical diagnosis.

36 Diagnosing a whole-system pressure fall

If source and endpoint pressures decline together during sustained additional demand, compare common-basis demand with verified usable supply. Check actual compressor state, pressure setting, availability, service condition and site performance limitations. Check for uncontrolled branches, major leaks and treatment consumption absent from the original accounting.

This pattern supports source-side or aggregate-demand investigation; it does not prove an undersized compressor. Confirm instruments and timeline. Recovery when a user stops is evidence of demand interaction, but corrective action still needs the duty and supply data. Identify whether the event is persistent or limited to a transition before proposing storage or another source.

37 Diagnosing a local pressure fall

If source pressure remains in its expected envelope while one endpoint falls, measure across intervening segments during the same event. Inspect final connections, valves, couplings, treatment path and hose extensions. Determine whether another user increases common-header losses at the same time.

Restore or redesign the evidenced restriction with approved components, then repeat the original scenario. Increasing source pressure without locating the loss may conceal the problem and raise pressure in other operating states. Link the corrective action to measured boundary differences, not solely to improved subjective spray appearance. Check whether the meter or temporary test assembly introduced a restriction.

38 Diagnosing oscillation and delayed recovery

Align machine events with compressor loading, regulator behaviour, pressure traces and concurrent users. Periodic pressure swings can arise from control interaction, rapidly varying demand or a supply path that cannot recover between events. The frequency and phase of observations help separate these possibilities.

Ask the relevant supplier to assess control settings and proposed storage or regulator changes. Avoid changing several variables simultaneously because attribution then becomes difficult. Repeat the same event sequence and compare before/after traces with the agreed criterion. A smoother average trace is insufficient if its lowest operating condition still fails the machine requirement.

39 Diagnosing water or oil observations

Identify where and when contamination was observed, the sampling method, pressure, temperature and operating mode. Investigate treatment condition, drains, downstream cooling, hose history, bypasses and branch contamination paths as appropriate. Visual observation may locate a problem but does not establish compliance with a numerical quality requirement.

Use suitable testing where acceptance depends on a contaminant limit. Retain sample handling and method with the result. Do not label every wet-material symptom as condensate; mix water, water-system faults and process conditions remain separate hypotheses. Recheck the delivery path after corrective work because contamination can remain downstream of the repaired source.

40 Air symptoms and process symptoms

An unsatisfactory spray pattern, fluctuating delivery or increased rebound may justify an air check, but none uniquely diagnoses the compressor. Review nozzle condition, feed consistency, material properties, water/additive settings and technique with the process owner. Record whether the air interface met its requirement during the event.

If the air duty passes while the process remains unsatisfactory, retain the evidence and escalate the process investigation. If air duty fails, correct the failure without promising a particular concrete outcome. Utility and placed-concrete acceptance are related records with different criteria and owners. Do not replace either with a visual judgement from an unrelated trial.

Troubleshooting decision matrix

41 Worked example conventions

Examples 1 to 5 are hypothetical teaching cases. Every numerical input is an invented case assumption, not a manufacturer rating, recommended shotcrete setting or universal allowance. The examples illustrate accounting, measurement interpretation and decision-making. Replace every input with job-specific evidence before selecting equipment.

Each case identifies its boundary and the consequence of missing information. None converts concrete output into air flow, guarantees spraying productivity or certifies a machine. All flows use one stated comparison basis unless the example explicitly demonstrates conversion. Retain these labels wherever examples are excerpted or reused.

42 Example 1 A transparent pressure budget

Assume a hypothetical machine requires at least 5.8 bar(g) at its inlet during the selected scenario. Assume validated losses at that flow of 0.25 bar across treatment, 0.35 bar in the common route and 0.20 bar in the final connection. The minimum source pressure for this assumed case is 5.8 + 0.25 + 0.35 + 0.20 = 6.60 bar(g). These are teaching inputs, not recommendations.

If the source’s documented lower operating point is 6.40 bar(g), calculated inlet pressure is 6.40 − 0.80 = 5.60 bar(g): a 0.20 bar shortfall. The result calls for an approved change and retest; it does not authorize a pressure increase. Check the machine’s maximum inlet limit, transient behaviour and available source flow at any revised pressure separately. No numerical reserve has been added.

43 Example 2 Simultaneous demand on one basis

Assume two hypothetical users require 5.5 and 4.0 m³/min on the same dry reference basis. An accessory requires 1.2 m³/min and separately evidenced treatment use is 0.4 m³/min. The combined demand is 5.5 + 4.0 + 1.2 + 0.4 = 11.1 m³/min at the source boundary. Assume supplier-confirmed site delivery is 10.6 m³/min at the pressure required by the governing route. The shortfall is 0.5 m³/min.

If the operating plan prohibits the accessory during both-user spraying, accounted demand becomes 9.9 m³/min. This result is conditional on the enforced scenario and resolution of every omitted demand; it is not a generic diversity factor or a complete selection pass. The 0.7 m³/min arithmetic difference in the restricted scenario is not an approved reserve.

44 Example 3 Normalizing two reference volumes

Assume dry ideal gas, equal compressibility factors and a hypothetical demand of 6.0 m³/min referenced to 1.01325 bar(a) and 273.15 K. Compare it with a quoted volume basis of 1.000 bar(a) and 293.15 K. Equivalent demand is 6.0 × (1.01325 ÷ 1.000) × (293.15 ÷ 273.15) = approximately 6.52 m³/min on the second basis.

A hypothetical source supplying 6.30 m³/min on that second basis would be short by approximately 0.22 m³/min before separately applicable consumption. Comparing 6.30 with the unconverted 6.0 would suggest the opposite. This example does not correct actual compressor performance for temperature or altitude. Obtain actual performance from the supplier, then compare it on a common basis. The dry-gas assumption must also match the compared data.

45 Example 4 What a receiver can bridge

Assume a rigid 1.0 m³ receiver initially at 8.0 bar(a), with lowest usable receiver pressure 7.0 bar(a). Assume isothermal ideal gas at the same temperature as the 1.0 bar(a) reference basis. Usable reference volume is 1.0 × (8.0 − 7.0) ÷ 1.0 = 1.0 m³. At a constant net deficit of 0.5 m³/min, idealized duration is 2.0 minutes.

Actual delivery may end sooner because of cooling during discharge, restrictions, control response and endpoint pressure needs. The lower receiver pressure must already account for the remaining delivery path. This is not vessel sizing or approval. It demonstrates finite storage: a sustained deficit continues after stored air is exhausted, and recharge requires spare capacity and time. Do not interpret the example duration as an operational hold-up guarantee.

46 Example 5 Moisture across a changing route

Assume a hypothetical treatment report records +3°C pressure dew point at the relevant line pressure. The route review identifies an exposed section that may reach −2°C at comparable pressure. Reported dew point is above the cold condition, so the record does not demonstrate avoidance of downstream condensation. These temperatures are example inputs, not a dryer recommendation.

Agree the required moisture performance, measurement point and worst conditions with the responsible suppliers, then assess treatment or route changes. If dew point was measured after expansion to atmospheric pressure, direct comparison is invalid and needs correction. No generic temperature margin is inserted. Record the required test method and which party will confirm performance at the stated condition.

47 Commissioning document readiness

Before testing, assemble the approved duty brief, machine/nozzle identity, route schedule, component information, scenarios, calibrated instrument list and criteria. Confirm the installed route matches the assessed route. List deviations and resolve those affecting the test boundary before claiming a pass.

Assign an owner to record the operating sequence and synchronize observations. Supplier and site responsibilities must be explicit, including authority to stop the test. Record what evidence is needed to release any hold point so commissioning does not depend on informal assumptions.

48 Commissioning the delivery path

Check identification, connections, condition and permitted operating limits through the approved inspection process. Confirm isolation, drainage, treatment path and absence of unintended cross-connections. Establish instrument readings at the planned source and endpoint locations.

Follow the permitted sequence and build to the agreed scenarios. Record stable conditions and transitions included in the duty. If a condition cannot be achieved without departing from supplier limits, record a nonconformance and refer it to the responsible owner. Do not improvise a setting to finish the test or silently shorten a test that reveals deterioration over time.

49 Testing the governing scenarios

Test complete concurrency, the demanding approved route and relevant source control conditions. Include an accessory joining or leaving where it belongs to the approved plan. Observe the endpoint during the event, not just after recovery. Record duration and why it represents the duty.

Testing a shorter hose or fewer users does not accept the larger configuration. If practical constraints prevent the governing test, document the gap and evidence required to close it. Do not replace missing evidence with verbal assurance. Preserve the same measuring arrangement and units when comparing candidate changes, or explicitly account for differences.

50 Acceptance and measurement uncertainty

Agree criteria before testing: pressure range at the named interface, flow and basis, relevant quality/temperature conditions, operating scenarios and any permitted transient envelope. The machine supplier or project authority supplies these limits.

Record measured values, uncertainty and outcome for each criterion. Use pass, fail or unresolved with a reason. A mean cannot satisfy a minimum if relevant dips fall below it. Excessive rounding must not hide uncertainty. Keep utility acceptance separate from process quality approval and state which untested operating states remain outside the acceptance.

51 Handover to operations

Give operators the accepted route, source settings, permitted concurrency, machine/nozzle identity, treatment arrangement and monitoring requirements. Show the measurement boundary and changes requiring review. Provide supplier and site procedure references rather than reproducing an incomplete operating manual.

Retain the completed brief, test records, deviations and approved resolutions. Operators should be able to check whether today’s arrangement matches the accepted configuration. Where hose extensions, additional tools or nozzle changes are common, make the change-control trigger clear. A signed record for an earlier arrangement is not a blanket release for all future site configurations.

52 Maintenance and recurring verification

Base maintenance on applicable equipment information and site conditions. Record inspection of hoses, fittings, drains, filters and measuring instruments, together with supplier-defined replacement or service triggers. Check new components against their original function, pressure limit and flow path, not just physical fit.

Compare recurring measurements with the baseline where duty is unchanged. Increasing differential pressure across a segment or changed contamination observations can direct investigation. They are diagnostic evidence, not proof of a universal replacement threshold. Record the configuration and demand when taking readings so changes in use are not mistaken for degradation.

53 Change control for a moving site

Reopen the brief when machine, nozzle, material, route, elevation, hose bore, source setting, treatment or concurrent users change. Record the reason, affected scenarios and necessary recalculation or retest. Do not carry an acceptance signature forward to a materially different system.

Preserve the superseded brief with its route and date. The replacement record should explain changed assumptions rather than overwrite them. Where the change stays within an approved envelope, record the evidence for that conclusion and the approving owner.

54 Energy and operating tradeoffs

Compare arrangements at the same verified duty. Options include reducing evidenced restrictions, repairing leaks, separating incompatible users, changing the operating sequence or selecting a source matched to demand. Quantify benefit using measurements or supplier performance, including treatment use and relevant hours.

A pressure reduction is acceptable only if all required endpoints remain within their approved envelope. Retain delivery and process boundaries during cost comparison. Reduced average consumption does not compensate for a failing peak scenario.

55 Procurement comparison and exclusions

Use a common response schedule: machine boundary, usable flow and basis, dynamic pressure, site conditions, treatment, route assumptions, controls, utilities and commissioning. State whether hoses, manifolds, meters and treatment are included. Compare the same delivery boundary rather than headline capacities.

Require explicit exceptions. A proposal excluding the final hose is not a guarantee at the machine inlet. Compressor-only supply retains that boundary in the purchase record, with a named owner for the remaining path. A revised proposal must identify which earlier assumptions it supersedes and whether the original acceptance plan still applies.

56 What air capacity cannot establish

An air-duty check does not approve the concrete mix, material transport system, nozzle technique, substrate preparation, structural design or placed-concrete properties. The relationship between air and placement performance requires collaboration but does not transfer those approvals to the compressor provider.

Keep productivity, rebound, strength, durability and safety claims outside the page unless separately supported in the exact claimed context. Do not describe a successful air test as compliance with a construction specification. State the tested utility condition and refer process outcomes to their own acceptance record. This boundary must survive marketing edits and shortened answer blocks.

57 FAQ How much compressor air is needed

Use the machine and nozzle supplier’s flow and pressure requirement for the selected process and operating condition. Normalize the flow basis, add separately applicable simultaneous demand and consumption, and check delivery losses and site capability.

If the requirement is incomplete, complete the Concrete Spraying Air Requirement Brief. Pump output or a previous job’s compressor size cannot close that evidence gap. A supplier assessment should name the configuration and relevant route rather than reply with an unqualified capacity.

58 FAQ Why can pressure look adequate at the compressor

The compressor reading describes one location. Delivery losses and changing demand can produce a different dynamic condition at the machine. Record simultaneous source and endpoint measurements under the specified duty, then investigate the intervening route if the endpoint requirement is not met.

A static reading after spraying stops does not demonstrate dynamic performance. Pressure alone also does not confirm flow or quality. The acceptance record must state the boundary, operating mode and measurement basis. Recovered pressure must not replace evidence of a dip during the required event.

59 FAQ Can wet and dry equipment share one supply

Assess sharing only after individual requirements, quality boundaries, pressure limits and simultaneous operation are defined. Process names alone establish neither compatibility nor combined capacity. Evaluate the common header and each branch under the actual scenarios.

Apply the same reasoning when replacing a hand nozzle with a mechanised assembly. Retain the new supplier data, update the brief and verify the changed configuration before carrying forward an earlier result. A shared source must also have clear ownership for changes made by each connected user.

60 FAQ What belongs in an enquiry

Provide machine/nozzle identity, process and material description, the supplier’s original air requirement and units, pressure location, route and elevation, site conditions, intended duration and scenarios, shared users, quality requirements and utilities. Attach the supporting manual or supplier statement with its revision.

Label unknown facts for confirmation and assign owners. Request a documented air-duty assessment. Completing the form does not by itself guarantee equipment suitability or spraying performance. Preserve the response and its qualifications with the final accepted brief.

Part B Concrete Spraying Air Requirement Brief

Complete this reusable enquiry and acceptance brief for one identified machine configuration and site arrangement. Use “not confirmed” for an unknown and “not applicable” only with a reason. Attach supporting evidence. Duplicate demand rows for additional users. Blank values are not approved values.

61 Project machine and evidence identity

62 Air requirements and demand register

Scenario total: __________ on basis __________ at boundary __________. Unresolved demand: __________. Prohibited or excluded concurrency and means of control: __________.

No automatic diversity or reserve multiplier applies. Any separately justified allowance must state purpose, evidence, value, approval and whether it is included elsewhere. Record the supply boundary before adding or subtracting treatment consumption.

63 Distribution and site schedule

64 Pressure budget and scenario decision

Governing scenario: __________. Other required scenarios: __________. Endpoint upper-limit check: __________. Control/transient assessment: __________.

Decision: suitable for specified assessment / changes required / unresolved. Reason and open actions: __________. Owner and evidence due: __________. The decision applies only to the exact recorded route and operating arrangement. An unresolved requirement prevents a final duty-selection claim.

65 Commissioning and acceptance record

Instrument IDs and calibration: __________. Date, duration and conditions: __________. Raw record location: __________. Deviations and resolutions: __________.

Utility acceptance owner/signature: __________. Machine/process acceptance owner/signature: __________. These approvals remain distinct. Changes requiring reassessment: __________. Untested states and restrictions: __________.

66 Enquiry wording and ownership

Reusable enquiry text: Please assess compressed air supply for the machine, nozzle and site arrangement recorded in this Concrete Spraying Air Requirement Brief. Confirm usable delivered flow on the stated reference basis, dynamic pressure at the named interface, air quality and temperature requirements, site performance, distribution assumptions and concurrent users. Identify all included items, exclusions and unresolved requirements. Provide supporting performance information and the proposed verification method. Do not substitute a generic shotcrete duty for the attached machine requirement.