Interactive resource
Use the working tool for this page
This page has a matching worksheet, calculator or comparison resource. It runs in your browser: enter your own measured values and keep the evidence behind every result.
Open resourceRequired asset: Dry Scroll Duty Worksheet
R01 decision: Match clean vacuum duty operating range and maintenance constraints.
R01 release gate: State the exact scroll model and applicable service restrictions.
1 Direct answer
A dry scroll vacuum pump should be matched to a defined clean-vacuum duty by using the exact model's pumping-speed curve across the required pressure range, then checking gas load, vessel pump-down, inlet conductance, ultimate pressure, particle and vapour exposure, ambient and inlet temperature, exhaust conditions, tip-seal maintenance, duty cycle, noise and service access. Ultimate pressure is a limiting test result under stated conditions; it is not the pumping speed available at the process operating pressure.
It does not create a universal ultimate pressure, pumping speed, water-vapour tolerance, particle limit, tip-seal interval, noise value or service restriction.
2 Controlled scope
It covers pressure range, pumping-speed curve, pump-down, continuous throughput, gas composition, particles, vapours, thermal conditions, controls and maintenance.
Process safety, hazardous-area compliance, materials compatibility, emissions, product qualification, electrical approval and final supplier selection remain with competent project disciplines and the exact manufacturer.
4 Dry scroll pumping principle
A dry scroll pump commonly uses one fixed and one orbiting scroll to form gas pockets that move toward discharge. Tip seals help separate adjacent pockets. The pumping chamber can operate without process-side oil in the documented design, while bearings or drive components may use lubricant outside that chamber.
The narrow internal geometry makes particles, deposits, thermal distortion and seal condition important. Dry compression does not mean unlimited contamination tolerance.
5 System boundary
Define the process vessel or tool, isolation valve, inlet trap or filter, hose and piping, pump inlet, pump, exhaust silencer or treatment, cooling path, purge or vent, controls and discharge destination. Identify pressure and temperature measurement points.
Include shared manifolds, check valves, bypasses and standby pumps. The effective speed at the vessel can be lower than pump-port speed because of conductance.
6 Operating states
State | Pump and process condition | Evidence purpose |
|---|---|---|
Isolated safe | Electrical and vacuum energy isolated | Maintenance starting condition |
Pre-start | Inlet path exhaust cooling and controls ready | Readiness confirmation |
Rough pump-down | Vessel pressure falls rapidly | High-pressure curve and motor load |
Low-pressure pump-down | Gas release and effective speed govern | Time-to-target evidence |
Continuous gas load | Stable throughput at working pressure | Working-speed acceptance |
Idle vacuum | Pump holds an evacuated system | Leakage outgassing and temperature |
Vapour event | Condensable load temporarily rises | Compatibility and procedure check |
Particle upset | Credible contamination occurs | Protection and inspection response |
Controlled shutdown | Vessel isolated or vented as required | Tip-seal and process protection |
Power loss or trip | Unplanned stop | Backflow and process response |
Service | Tip seals filters and internals addressed | Access and contamination control |
Restart | Approved readiness restored | Repeatability after stop or service |
7 Pressure definitions
Use absolute pressure for pumping curves, ultimate pressure and throughput. Record gauge pressure only when operationally useful. State the instrument location and accuracy.
Vessel pressure, manifold pressure and pump-inlet pressure can differ. Pressure loss in the inlet path reduces effective speed and can distort a curve comparison.
8 Ultimate pressure
Ultimate pressure is the lowest pressure documented under stated test conditions, often with a defined blank-off arrangement and gas condition. It does not establish the speed available at a higher working pressure, nor the installed system's achievable base pressure.
Leaks, outgassing, permeation, vapour and instrument limits can hold the system above the pump's ultimate pressure. Use the actual application gas load and curve.
9 Pumping-speed curve
Use the exact model and frequency curve. Identify speed at the required inlet pressure and across the pump-down range. Record curve tolerance, gas, temperature, inlet arrangement and test standard when available.
A headline nominal speed can be a maximum or plateau value. It should not be applied unchanged near ultimate pressure.
10 Effective speed at the vessel
Pump-port speed and inlet conductance combine to determine effective speed. In simplified molecular-flow form, reciprocal effective speed equals reciprocal pump speed plus reciprocal conductance, but the valid conductance model depends on pressure regime and geometry.
Measure or calculate the inlet path using an appropriate method. Short, wide and clean connections generally preserve more speed than long restrictive ones.
11 Pump-down duty
Pump-down is defined by vessel and connected volume, starting pressure, target pressure, allowed time, gas release, leakage and pumping speed versus pressure. Valve timing and instrumentation also affect the measured time.
For an idealised constant effective speed with negligible gas load, time equals vessel volume divided by effective speed multiplied by the natural logarithm of starting pressure divided by final pressure. Real assessment should integrate the curve and gas load.
12 Continuous gas-load duty
Continuous duty is governed by gas throughput at the target pressure. In consistent units, throughput equals pressure multiplied by pumping speed. The required speed equals throughput divided by allowable pressure.
A pump that evacuates a vessel acceptably can still fail a continuous load if working-speed capacity is insufficient. Conversely, a continuously loaded pump may not meet a rapid pump-down time.
13 Gas throughput and flow basis
State mass flow, reference volume, actual inlet volume or throughput with pressure and temperature. In vacuum work, mbar L/s or Pa m3/s can represent gas throughput and should not be confused with volumetric pumping speed.
Preserve units through each calculation. Convert only with a stated gas model and reference state.
14 Leakage outgassing and permeation
Separate real leaks, virtual leaks, desorption, permeation and process gas release where relevant. A pressure-rise test, helium leak test or other method requires a defined procedure and acceptance source.
Outgassing can dominate low-pressure pump-down even when the mechanical pump has adequate nominal speed. Materials, surface area, temperature and cleanliness matter.
15 Particle sensitivity
Particles can damage tip seals, score surfaces, increase leakage and alter clearances. Record particle composition, size, concentration and credible upset load.
Use inlet filtration, traps or process controls supported by the exact model and process. A filter adds conductance loss and requires maintenance.
16 Powder and process carryover
Fine powder, fibres and fragments can travel during venting, tool motion or rapid evacuation. Design the connection and operating sequence to limit carryover.
A clean-vacuum scroll duty should not be released when routine solids ingestion is expected without explicit manufacturer approval and a credible protection and service plan.
17 Vapour handling
Record vapour identity, concentration, dew point, load profile and cleaning chemistry. Determine whether vapour can condense in the inlet, scroll set, exhaust or shutdown state.
Use exact model restrictions and any documented purge or operating procedure. Dry pumping does not establish compatibility with solvents, water vapour or reactive condensables.
18 Condensation and liquid ingress
Liquid droplets or in-pump condensation can damage seals, cause deposits or create corrosion. Provide traps, separators, controlled warm-up or purge when required by the approved design.
Define drain and waste handling. Do not restart repeatedly after liquid ingress without the specified inspection or recovery procedure.
19 Corrosive reactive and toxic gas
List all constituents and upset cases. Review scroll materials, tip seals, gaskets, exhaust and downstream treatment. Consider containment and safe service.
A chemical-resistant version for one medium does not prove compatibility with mixtures or higher temperature. Obtain written confirmation.
20 Tip seals
Tip seals are functional wear components in many dry scroll designs. Their condition affects pumping speed, ultimate pressure, noise and power. Record exact material, service method and replacement criteria.
Follow the exact model manual and adjust planning for duty, pressure, particles, vapours, temperature and start frequency.
21 Maintenance planning
Convert documented service tasks into site work: isolation, venting, decontamination, access, tools, parts, labour competence, time and post-service checks. Record whether tip-seal work is field-permitted or requires an authorised service route.
A service interval stated for clean laboratory duty may not apply to process exposure. Track operating hours and condition evidence.
22 Post-service verification
After maintenance, verify assembly, rotation where applicable, inlet integrity, sound, current or power, pump-down and base pressure against approved criteria. Confirm counters and alarms are reset correctly.
A new tip seal does not close an unresolved particle or vapour source. Correct the cause before returning to unrestricted duty.
23 Temperature and cooling
Record inlet, exhaust, housing and ambient temperature limits from exact documentation. Confirm ventilation clearance and any fan or cooling path.
High inlet load, restricted exhaust, deposits, enclosure recirculation or altitude can increase temperature. Do not invent a universal ambient derating.
24 Exhaust and backpressure
Silencers, filters, condensers and common exhausts can create backpressure. Check the exact allowable outlet condition and service-state pressure loss.
Manage exhaust gas, vapour, particles and trace emissions according to process and environmental requirements. Atmospheric discharge is not an automatic assumption.
25 Noise and acoustic context
Use documented sound data only with model, speed, test method, pressure condition and enclosure. Installed sound changes with exhaust treatment, structure, piping and room reflection.
Record the site criterion and measurement position. A change in sound can also be a maintenance symptom.
26 Vibration mounting and piping
Install on a suitable support and avoid unacceptable piping strain. Flexible connections and isolation should follow the exact installation instructions and process needs.
Trend vibration only with a defined measurement method and baseline. Do not invent a universal limit.
27 Motor electrical and controls
Check voltage, frequency, motor rating, start method, current, protection, ambient, altitude and enclosure. Define remote start, run status, alarms and process permissives.
Variable-speed operation, if available, must remain within the exact model envelope. Control changes affect pump-down, working speed, temperature and noise.
28 Starts duty cycle and standby
Record starts per period, continuous-hour limits, standby strategy, venting and restart. Frequent starts may affect motor and thermal condition.
If vacuum must be retained during standby or power loss, define isolation and backflow prevention from exact system requirements.
29 Instrumentation
Measure vessel and pump-inlet pressure where conductance matters. Select gauge technology and range appropriate to the pressure band and gas.
Record calibration status, response, zero, gas sensitivity and data acquisition. A single broad-range gauge may not resolve every acceptance point.
30 Protection and interlocks
Define inlet pressure, temperature, current, cooling, exhaust and process permissives as required. Specify trip and alarm values from approved sources.
Protect against blocked exhaust, liquid carryover and unsafe gas where credible. The pump alone does not provide the complete process safeguard.
31 Clean-vacuum boundary
Define clean by process evidence: allowed particles, vapour, oil backstreaming, biological burden or product residue as applicable. Avoid an unqualified clean or oil-free label.
The pump may reduce one contamination source while remaining sensitive to what the process sends into it.
32 Selection sequence
Define the exact model candidate and duty. Establish pump-down and continuous gas-load requirements separately. Obtain the pumping curve, calculate effective speed, check ultimate pressure, then apply media, particle, vapour, temperature, exhaust, electrical, noise and maintenance gates.
Use a qualification hold when exact service restrictions or curve data are missing. Do not substitute a similar scroll model.
33 Diagnostic method
Symptom | Evidence to examine | Engineering direction |
|---|---|---|
Pump-down slows | Curve, conductance, leaks, outgassing, filter | Separate pump and system effects |
Base pressure rises | Tip seals, leakage, vapour, gauge condition | Perform approved condition checks |
Noise changes | Tip seal wear, bearing condition, exhaust, mounting | Compare with model baseline |
Current rises | Pressure load, deposits, restriction, temperature | Stop if required and diagnose safely |
Temperature rises | Ambient, ventilation, gas load, exhaust | Restore documented thermal condition |
Particle found | Process source, filter integrity, vent sequence | Prevent recurrence before restart |
Vapour residue appears | Dew point, process load, purge, shutdown | Review compatibility and procedure |
Performance drops after service | Assembly, seals, leak, counter, test method | Repeat post-service verification |
34 Commissioning and acceptance
Confirm exact model, curve, serial identity, inlet system, exhaust, electrical supply, controls, instruments and maintenance plan. Inspect cleanliness, filter condition, piping support, ventilation and access.
Capture pump-down, continuous-load, idle and shutdown states as applicable. Record pressure traces, gas load, time, current or power, temperature and deviations. Acceptance must use the stated model and service restrictions.
35 Worked case A pump-down requirement
Assumptions. A fictional clean vessel and connected volume total 0.600 m3. It must pump from 1000 mbar absolute to 10 mbar absolute within 240 s. A named fictional scroll model has 60 m3/h pump-port speed over part of the range; the installed inlet path gives a simplified effective speed of 55 m3/h for an initial screening. Gas release and leakage are temporarily neglected.
Method. Convert 55 m3/h to 0.01528 m3/s. Idealised time equals 0.600 divided by 0.01528 multiplied by the natural logarithm of 1000 divided by 10. The result is approximately 181 s.
Result and interpretation. The simplified screen is about 59 s inside the fictional requirement. Release is not justified by this calculation alone because real speed changes with pressure and outgassing, leakage, gauge response and valve timing add load. The exact model curve must be integrated or tested.
36 Worked case B continuous gas load
Assumptions. The same fictional model is considered for a continuous throughput of 120 mbar L/s at a required pump-inlet pressure no higher than 8 mbar absolute. The exact fictional model curve documents 50 m3/h at 8 mbar, equal to 13.89 L/s.
Method. Required speed is throughput divided by pressure: 120 divided by 8 equals 15 L/s, or 54 m3/h. The documented curve provides 50 m3/h. With 120 mbar L/s and 13.89 L/s, the ideal equilibrium pressure would be approximately 8.64 mbar before conductance loss.
Result and interpretation. The candidate fails this continuous-load screen even though it passed the simplified pump-down screen. Pump-down and continuous gas-load requirements are separate. Another model or system arrangement requires documented review.
37 Worked case C inlet conductance
Assumptions. The continuous-load case has a pump-port speed of 13.89 L/s and a fictional inlet conductance of 100 L/s at the relevant regime. The simplified reciprocal relation is used only for screening.
Method. Effective speed equals the reciprocal of one divided by 13.89 plus one divided by 100, giving approximately 12.20 L/s or 43.9 m3/h. The predicted vessel-side pressure for 120 mbar L/s becomes approximately 9.84 mbar.
Result and interpretation. A seemingly generous inlet conductance still reduces effective speed enough to move the duty further from the 8 mbar requirement. The valid conductance method and actual geometry must be confirmed.
38 Duty comparison
Item | Pump-down duty | Continuous gas-load duty |
|---|---|---|
Primary requirement | 0.600 m3 from 1000 to 10 mbar in 240 s | 120 mbar L/s at no more than 8 mbar |
Simplified required basis | Effective speed and logarithmic pressure range | Throughput divided by pressure |
Fictional model evidence | 55 m3/h simplified effective speed | 50 m3/h at 8 mbar pump port |
Screening result | Approximately 181 s | 54 m3/h required versus 50 available |
Conductance effect | Requires curve integration | Effective speed falls to about 43.9 m3/h |
Controlled disposition | Continue model-specific qualification | Fail current screen and reassess |
39 Maintenance planning example
Assumptions. A fictional exact-model manual states an 8000 operating-hour tip-seal inspection or replacement interval for a defined clean duty. The planned application operates 6000 h/year. The site has one annual planned outage but no accepted particle or vapour exposure.
Method. Pure hour division gives approximately 1.33 years to 8000 h. The maintenance owner must reconcile this with the annual outage, calendar restrictions, condition evidence, spare availability and the exact manual.
Result and interpretation. The calculation supports planning only. It does not extend the manual interval, and any contamination or abnormal condition can trigger earlier inspection.
40 Required asset Dry Scroll Duty Worksheet
Use this editable worksheet for screening, qualification and release. Record the exact scroll model in every completed version. Unknown restrictions remain open.
Worksheet A identity and boundary
Input or evidence field | Project entry | Owner reference and disposition |
|---|---|---|
Site process and duty owner | ||
Exact scroll manufacturer and model | ||
Serial configuration frequency and revision | ||
Functional objective | ||
Vessel piping and effective volume | ||
Inlet and exhaust boundaries | ||
Included traps filters valves and manifolds | ||
Operating states and availability |
Worksheet B pressure curve and gas load
Input or evidence field | Project entry | Owner reference and disposition |
|---|---|---|
Starting target and ultimate pressure | ||
Pressure measurement points | ||
Exact pumping-speed curve and revision | ||
Pump speed at each working pressure | ||
Inlet conductance and effective speed | ||
Continuous throughput and units | ||
Pump-down calculation and assumptions | ||
Leakage outgassing and permeation | ||
Acceptance time and working pressure |
Worksheet C media particles and vapours
Input or evidence field | Project entry | Owner reference and disposition |
|---|---|---|
Gas composition and variability | ||
Particle size concentration and source | ||
Powder fibre or process carryover | ||
Vapour identity load and dew point | ||
Liquid ingress and condensation controls | ||
Corrosive reactive or toxic constituents | ||
Product contamination limits | ||
Traps filters purge and cleaning method | ||
Written model-specific compatibility evidence |
Worksheet D temperature exhaust and utilities
Input or evidence field | Project entry | Owner reference and disposition |
|---|---|---|
Inlet exhaust ambient and housing temperatures | ||
Ventilation and cooling clearances | ||
Exhaust backpressure and service loss | ||
Silencer filter condenser and discharge route | ||
Electrical supply motor and starting | ||
Control mode speed and duty cycle | ||
Alarms trips permissives and integration | ||
Standby venting and backflow prevention | ||
Noise criterion and measurement basis |
Worksheet E tip seals maintenance and access
Input or evidence field | Project entry | Owner reference and disposition |
|---|---|---|
Exact tip-seal type and service instruction | ||
Documented interval and duty restrictions | ||
Operating-hour counter and condition evidence | ||
Field service or authorised service route | ||
Isolation venting and decontamination | ||
Access tools lifting and work time | ||
Spares storage and traceability | ||
Post-service leak and performance checks | ||
Abnormal-event inspection triggers |
Worksheet F qualification and release
Requirement | Evidence result | Status owner and closeout |
|---|---|---|
Exact model identified | Pass conditional fail or open | |
Pump-down duty accepted | Pass conditional fail or open | |
Continuous gas load accepted | Pass conditional fail or open | |
Working-speed curve accepted | Pass conditional fail or open | |
Particle restriction accepted | Pass conditional fail or open | |
Vapour and liquid restriction accepted | Pass conditional fail or open | |
Temperature exhaust and noise accepted | Pass conditional fail or open | |
Tip-seal plan and access accepted | Pass conditional fail or open | |
Applicable service restrictions stated | Exact document and revision | |
Final authorised selection release | Name role date and conditions |
41 Filled fictional worksheet extract
Field | Example entry | Controlled disposition |
|---|---|---|
Exact model | Scroll model DS-Example fictional | Example only |
Pump-down screen | 181 s versus 240 s requirement | Continue curve integration |
Continuous load | 54 m3/h required versus 50 m3/h curve | Fails current screen |
Conductance | Effective speed about 43.9 m3/h | Vessel pressure worsens |
Media | Clean dry non-corrosive gas assumed | Must be confirmed |
Tip seals | Fictional 8000 h clean-duty instruction | Duty restrictions apply |
Release | Not released | Select or assess another documented option |
42 Frequently asked questions
Is ultimate pressure the working pressure
No. Ultimate pressure is documented under specific test conditions. Working pressure depends on gas load, pumping speed, conductance, leaks and outgassing.
Can one pump pass pump-down but fail continuous duty
Yes. Pump-down depends on volume and speed across a pressure range. Continuous duty requires enough speed for the ongoing throughput at the target pressure.
Does dry scroll mean particle tolerant
No. Particles can wear tip seals and damage surfaces. Use the exact model restriction and required inlet protection.
Can a dry scroll handle water vapour
Only within the exact model's stated restrictions and approved operating procedure. Condensation and liquid ingress remain separate risks.
Are tip-seal intervals fixed
No universal interval applies. Use the exact model manual, duty restrictions, operating hours and condition evidence.
Can a similar model curve be substituted
No. The release gate requires the exact scroll model and applicable service restrictions.
Sources and evidence basis
3 Source and evidence basis
The governing R01 map fixes the title, decision, asset, depth, worked comparison, release gate and navigation. A supplied scroll brochure can support only its named model, revision, configuration and test conditions. Similar appearance or technology does not transfer a limit between models.
Production content must cite the exact model curve, manual, service instructions and written compatibility evidence. Every number in the worked cases is hypothetical and does not represent a customer result or available product.