Why scope matters more than the compressor size
Two rental offers for “one 900 cfm compressor” can be very different things. One may be a machine delivered to the gate. The other may be an installed, serviced and operated air station with dryers, hoses, fuel management and breakdown cover. Their headline capacities look the same, but their real cost and risk to the project are not.
Problems on site usually come from gaps no one owned: the hose that was too short, the dryer no one ordered, the crane that was not booked, the diesel that ran out on a Sunday. A clear scope prevents those gaps by tying every item to the requirement it serves and to a named party.
Separate the requirement from the equipment offered
Begin with what the process needs, not with a machine description. A good requirement states:
- Normal and maximum useful airflow, in cfm or m³/min.
- Pressure required at the delivery point, in bar and psig.
- Air quality, for example a pressure dew point or an ISO 8573-1 class.
- Operating hours per day, hire duration and likely extensions.
- Duty after a failure: is a standby needed, or can the plant accept a pause?
The proposal then lists the equipment and services that meet it. Each item should link back to the requirement. “One 900 cfm compressor” does not say at what pressure that flow applies, at what inlet conditions, or whether dryer purge and hose losses have been allowed for. “900 cfm free air delivery at 7 bar (101.5 psig), delivering at least 850 cfm at 6.5 bar at the plant tie-in after treatment” is a scope that can be checked.
Our temporary air duty specification page explains how to write the requirement.
Define the delivery boundary
State where responsibility for the air changes hands. Typical boundaries are:
- The compressor discharge valve.
- The outlet of the treatment train (after dryer and filters).
- The end of the supplied hose or manifold.
- A named tie-in point on the plant’s permanent pipework.
Pressure, flow and quality are then guaranteed at that boundary, not somewhere else. If the supplier’s scope ends at the compressor and the plant provides a long hose, the plant owns the pressure drop. Write it down, with a sketch if possible.
What should a rental scope include?
List equipment and services by function, so that nothing is assumed.
| Function | Typical items | Question to settle |
|---|---|---|
| Compression | Compressors, standby units | Rated flow at what pressure; diesel or electric; oil-injected or oil-free |
| Treatment | Aftercooler, separator, dryer, filters, condensate drains | Required dew point and class; who disposes of condensate |
| Storage and distribution | Receiver, manifold, hoses, couplings, valves | Lengths, sizes and connection type at the tie-in |
| Power and fuel | Generator, cables, distribution board, diesel supply | Who supplies, connects and pays for electricity or fuel |
| Transport and handling | Delivery, crane or forklift, positioning, return | Who books and pays for lifting; access route |
| Operation | Operators, shift cover, daily checks | Number of shifts; who starts, stops and logs |
| Maintenance | Servicing, oil, filters, breakdown attendance | Service interval; what consumables are included |
| Site work | Foundations, barriers, tie-in welding, permits | Who prepares the ground and makes the plant connection |
Make exclusions specific and actionable
An exclusion such as “civil works by client” is too vague. A useful exclusion names the item, the party responsible and the deadline:
- “Level hardstanding for two compressors and one dryer, 10 m × 6 m, prepared by the client before delivery.”
- “Tie-in flange on the plant main with isolation valve, provided by the client’s mechanical contractor.”
- “Diesel fuel supplied by the client; refuelling carried out by our operator.”
- “Electrical connection from the client’s board to the compressor, by the client’s licensed electrician.”
Review every exclusion with one question: if this item is not done, can the air be delivered? If the answer is no, it must be someone’s responsibility with a date.
Power, fuel, operators and maintenance
These four items cause most disputes on long hires.
Power and fuel: state whether the client provides grid power or diesel, who connects it, and who monitors fuel levels. Running out of diesel is one of the commonest causes of an avoidable stop. Our fuel supply and refuelling page covers this in detail.
Operators: say whether the hire is “dry” (machine only) or includes operators, how many shifts they cover and what they are expected to do. An operator who starts, stops, logs and does daily checks is different from a technician who can diagnose and repair.
Maintenance: state the service interval and what is included. On our hire jobs we service machines every 300 running hours, with oil changes and filter replacement, and attend breakdowns. Say who supplies oil, filters and separator elements, and whether consumption due to dusty or hot conditions is covered.
Standby and replacement: distinguish a standby unit on site, ready to start, from replacement support, which means a machine sent after a failure. They give very different protection.
Commissioning, acceptance and the charging basis
Agree how the air station will be accepted before production relies on it. A simple acceptance check confirms flow, pressure at the boundary, dew point where specified, alarms and safety shutdowns, and records the readings. See commissioning and acceptance.
Then state how time is counted. Typical questions are:
- Does the hire start on dispatch, on arrival or on accepted commissioning?
- Is it charged per day, per week, per month or per running hour, and is there a minimum period?
- How are standby days, idle days and stoppages caused by site conditions treated?
- How are extensions agreed, and with how much notice?
- When does the hire end: on stopping, on disconnection or on return to the depot?
Compare offers on an equal scope
To compare rental proposals fairly, put them on the same duty and the same responsibility schedule. Add the cost of every item one offer includes and another excludes: treatment, hoses, transport, operators, fuel, electricity and servicing. Then add the energy cost of running the station for the expected hours, using kWh for electric units and litres of diesel for engine-driven units. A machine that delivers the required pressure with less unloaded running uses less fuel or power over a long hire.
A compressor-only offer may look cheaper per day and still cost more once the missing items are bought separately, or once a stoppage occurs because no one was responsible for them.
Changes, deviations and return
Site conditions change: demand rises, the hire is extended, a second shift starts or the station has to move. Treat each as an engineering change. Confirm whether the existing machines still meet the new duty, whether treatment and hoses still suit, and how the change affects time and charges.
Write down any assumptions the offer relies on, such as ambient temperature, inlet conditions, access or available power. If an assumption turns out to be wrong, both parties know where they stand.
At the end, define how the equipment is returned: who disconnects and makes safe the tie-in, who reinstates the ground, and how the condition of the equipment is recorded. Our demobilisation and return page explains the steps.
A final scope schedule you can use
- Requirement: flow, pressure, quality, hours, duration, failure duty.
- Delivery boundary, with a sketch.
- Equipment by function, with ratings at the working pressure.
- Services: transport, installation, commissioning, operation, maintenance, breakdown.
- Client responsibilities with deadlines: ground, power, fuel, tie-in, permits, security.
- Exclusions, each with the party that will provide the item.
- Acceptance method and records.
- Time and charging basis, including extensions and end of hire.
- Assumptions and how changes are handled.
How Reddy Compressors helps
Since 2002 we have supplied, rented and serviced compressors of ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and other makes as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands. Our own rental fleet covers 50–2,000 cfm at 2–30 bar, diesel and electric, oil-injected and oil-free, and for long-term projects we can supply brand-new machines to site.
When we quote, we:
- State flow and pressure at a defined boundary, and list treatment, hoses and accessories by function.
- Make clear what we provide and what the client provides, including fuel, power, lifting and tie-in.
- Offer operators where needed, servicing every 300 running hours and breakdown attendance.
- Arrange generators through Reddy Generators, under the same management, when power is needed.
Our past scopes have ranged from a single 400 cfm compressor with a 25 kVA generator for an infrastructure contractor at Raichur to a complete temporary power-and-air package for a natural-gas development at Kakinada, which included compressors, generators, distribution boards, operators, a technician, erection, commissioning and transport. Our team of more than 20 service engineers and technicians works from Tarnaka, Secunderabad across Telangana and Andhra Pradesh, with supply across India.
What to send us
- Required flow, pressure at the point of use and air quality.
- Where you want our responsibility to end.
- Hours of operation, duration and likely extensions.
- Whether you need operators, standby units or generators.
- What you can provide on site: power, fuel, lifting, ground preparation, tie-in.
- Site location and access details.
Frequently asked questions
What is included in a compressor rental?
It varies between suppliers, which is why the scope must be written down. A basic hire may cover only the compressor. A fuller package can include treatment, hoses, receiver, transport, installation, operators, servicing and breakdown cover. Ask for a list by function and check who provides fuel or power, lifting, the plant tie-in and condensate handling.
What is a dry hire compressor?
Dry hire usually means the machine is supplied without an operator, and often without fuel; the client runs it and does daily checks. Wet or operated hire includes operators and sometimes fuel. Servicing and breakdown attendance may still be included in a dry hire, so confirm exactly what the supplier will do during the hire period.
How do I compare two compressor rental quotes?
Put both on the same duty: flow at the same pressure and delivery point, the same air quality and the same hours. Then list everything each offer includes and excludes, and add the cost of missing items such as dryers, hoses, transport, operators and fuel. Finally add the expected energy or diesel consumption over the hire.
Who is responsible for fuel on a diesel compressor hire?
Either party can be, but it must be stated. Often the client supplies diesel and the operator or supplier refuels and monitors levels. Running out of fuel is a common and avoidable cause of stoppage, so agree who checks the level, how often, and what reserve is kept on site, especially for night and weekend work.
When does compressor hire start and end?
That depends on the agreed basis. Hire may start on dispatch, on arrival or on accepted commissioning, and may end on stopping, disconnection or return. State the rule in the scope, along with any minimum period, how idle days are treated and how extensions are agreed, so there is no dispute at the end of the job.
Why should exclusions name who provides each item?
An excluded item is still needed if the air is to be delivered. Naming who provides it and by when turns an exclusion into an action. Without that, items such as ground preparation, electrical connection or the tie-in flange are often left until delivery day, when they delay the start of service.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.