Why technical contract terms matter
Many compressed-air disputes start after the machine arrives. The purchase order said “500 cfm at 7 bar”, the plant measured less, and the supplier points out that the figure was at different inlet conditions, excluded the dryer, or applied to the airend rather than the package. Without a defined boundary and method, neither side can prove its case.
Good technical contract terms protect both buyer and supplier. They carry the technical basis agreed at bid evaluation through to installation, commissioning and handover, so that nothing accepted at award is quietly lost later. This page covers the engineering side of that work. Commercial and legal terms need review by the buyer’s own contract and legal advisers.
Freeze the accepted technical basis
At award, collect everything that was technically agreed into one controlled attachment to the contract. It should include the specification, the supplier’s technical offer, all clarifications and all accepted deviations. See procurement, technical specification and bid evaluation for how that basis is built.
- Requirements traceability: list each critical requirement and show where it appears in the specification, supplier response, contract, drawings and acceptance test.
- Deviation register: every accepted deviation, written down, so it does not depend on anyone’s memory of the bid meeting.
- Clarification register: answers to technical queries, with dates.
- Document precedence: contract and legal teams set the order of precedence; engineering should flag any conflicting technical documents before execution.
- Change control: a requirement accepted at evaluation should not disappear through informal emails or site discussions.
Define scope and battery limits
Battery limits state physically and functionally where the supplier’s responsibility starts and ends. Unclear limits are a frequent cause of delay: nobody ordered the flexible hoses, the drain manifold, the control cable or the foundation bolts.
| Interface | Typical questions to settle |
|---|---|
| Compressed air | Outlet flange size and rating, isolation valve, flexible connection, non-return valve |
| Electrical | Incoming supply point, starter or drive, cable sizes, earthing, who terminates |
| Cooling and ventilation | Ducting, fans, cooling water connections and water quality |
| Condensate | Drain lines, manifold, oil–water separator, discharge point |
| Controls and data | Sequencer, remote signals, network connection, cybersecurity responsibility |
| Civil | Plinth, anchors, lifting beams, openings |
Write separate lists for buyer-supplied scope, supplier scope and any installation contractor’s scope, and a clear list of exclusions. Buyer obligations matter because supplier guarantees often assume them, for example a maximum room temperature or a stable voltage.
What should a compressor performance guarantee cover?
State precisely what is guaranteed. Typical guaranteed parameters include:
- Free air delivery (FAD) at a stated working pressure, measured at the package outlet
- Total package input power, or specific power in kW per m³/min, at the same point
- Pressure dew point at the dryer outlet, for example a refrigerated dryer at typically about +3 °C or a desiccant dryer at −20 °C or −40 °C, at stated inlet conditions
- Pressure drop across dryers and filters at rated flow
- Air quality at a defined sampling point, expressed as ISO 8573-1 classes
- Noise level at a defined distance and conditions
- Control performance, such as pressure band held by a sequencer
For each item, record the reference conditions: inlet temperature, inlet pressure, humidity, cooling-water temperature where relevant, and the pressure at which flow and power apply. State which auxiliaries are included in the power figure: main motor, fan motor, drive losses, dryer and controls.
Measurement method and tolerances
Compressor flow and power are normally tested to a recognised standard such as ISO 1217, which also sets measurement tolerances. Agree before award:
- Which test standard applies, and which edition
- Whether the test is at the factory, on site, or both
- The instruments to be used, their calibration and who provides them
- How site readings will be corrected to the guarantee reference conditions
- The tolerance on each parameter, separate from measurement uncertainty
- Who witnesses the test and signs the record
Site tests are valuable but harder to control. Ambient conditions, leaks, other compressors and instrument installation can all affect results. Where site testing is the acceptance basis, define how the compressor will be isolated and how stable conditions must be before readings count.
Pre-delivery checks and documentation
Before dispatch, the buyer should receive and review:
- General arrangement and foundation drawings
- Piping and instrument diagram for the package and treatment
- Electrical schematics and cable schedules
- Data sheets for the compressor, dryer, filters and receivers
- Factory test reports where agreed
- Pressure vessel documentation and safety valve certificates, as required
- Recommended spares list and maintenance schedule
Approval of drawings is a technical check, not acceptance of performance. Make that distinction clear in the contract.
Site acceptance: commissioning and performance testing
Acceptance should happen in clear stages, each with its own record:
| Stage | What is checked | Typical evidence |
|---|---|---|
| Mechanical completion | Installed per drawings, connections, supports, clearances, drainage | Signed checklist, photographs |
| Pre-commissioning | Rotation, oil levels, electrical tests, safety devices, alarms | Test sheets, settings record |
| Commissioning | Start-up, load and unload, controls, sequencing, trips | Commissioning report with parameters |
| Performance test | Guaranteed parameters at agreed conditions | Test report against the agreed method |
| Reliability run | Continuous operation without significant faults for an agreed period | Run log, fault history |
| Handover | Documents, training, spares, punch list closure | Handover certificate |
See commissioning, start-up and acceptance and handover and documentation for the detail of each stage.
When a guarantee is not met
The contract should say in advance what happens if a guaranteed parameter is missed. Engineering input helps define realistic options:
- Investigation to check whether the shortfall is real or caused by test conditions or site interfaces
- Rectification by the supplier within an agreed period
- Retest using the same method
- Agreed commercial remedies, which are a matter for the contract and legal teams
- Right of rejection in defined circumstances
Keep the technical record factual: measured values, conditions, corrections and uncertainty. A clear record makes resolution quicker for both sides.
Defects liability and after-sales obligations
Technical terms should also cover the period after handover: the defects liability period agreed in the contract, the response expected for faults, availability of spare parts, who carries out routine maintenance during that period, and how warranty conditions such as approved lubricants and service intervals are recorded. If the plant or an independent service provider maintains the machine, agree in writing what records are needed to keep warranty cover valid.
Common contract gaps
- Flow stated without pressure or reference conditions
- Power quoted as motor shaft power rather than total package input
- Dryer dew point stated without inlet temperature and flow
- No agreed test method or tolerance
- Buyer responsibilities missing, so supplier assumptions are never checked
- Battery limits shown only on a sketch nobody signed
- Training, spares and documents listed as “as required”
How Reddy Compressors helps
As an independent multi-brand compressor specialist based in Tarnaka, Secunderabad, we work with buyers and suppliers on compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes. We are not an authorised dealer for any brand, which lets us take a neutral technical view. We have tie-ups with all major and reputed brands.
When we supply new or used compressors, rentals or project packages, we set out the duty, battery limits and commissioning steps clearly in our offer. For buyers procuring from others, we can help review technical specifications and offers, check that guarantees state their basis, and support site commissioning and performance checks. Our service teams cover Telangana and Andhra Pradesh, and we support projects across India where feasible. We do not provide legal advice; commercial and legal terms remain with your own advisers.
What to send us
- Your technical specification and the supplier offers or contract technical attachment
- The guaranteed parameters and any stated test method
- Drawings showing battery limits and interfaces
- Site conditions: ambient, power supply, cooling and ventilation
- Project timeline for delivery, installation and commissioning
- Any measured results or disputes you need help interpreting
Frequently asked questions
How do I check that a new compressor delivers its rated FAD?
Agree the test method before purchase, normally based on ISO 1217, including the working pressure, reference conditions, instruments and tolerances. On site, isolate the compressor from other machines and leaks, let it stabilise, and measure flow, pressure, inlet conditions and power together. Correct the readings to the guarantee conditions and compare against the guaranteed value with its agreed tolerance.
What should be included in a compressor purchase specification?
Include the required FAD at a stated working pressure, site ambient and altitude, air quality as ISO 8573-1 classes, operating pattern, power supply, cooling method, controls and communication, noise limit, battery limits, documentation, training, spares and the acceptance test method. State which auxiliaries count in the guaranteed power and ask suppliers to state reference conditions for every performance figure.
Is compressor power measured at the motor or for the whole package?
It depends on what the contract says, which is why it must be specified. Motor shaft power excludes fan motors, drive losses, dryer power and controls, so it makes the package look more efficient. For a fair comparison and guarantee, specify total package input power at the stated working pressure, and compare suppliers on specific power in kW per m³/min of FAD.
Who is responsible if a compressor overheats because of poor room ventilation?
That depends on the battery limits and buyer obligations in the contract. If the supplier’s guarantee assumed a maximum room or intake temperature and the buyer was responsible for ventilation, an overheating problem may fall on the buyer. Write room conditions, ventilation responsibility and duct limits into the contract so this question has a clear answer before installation.
What is a reliability run in compressor commissioning?
A reliability run is a period of continuous operation after commissioning, during which the compressor must run without significant faults or trips under normal plant conditions. Its length and acceptance criteria are agreed in the contract. It confirms that the machine, controls and site interfaces work together in real service, beyond a short performance test.
Can an independent service provider maintain a compressor under warranty?
Often yes, but it depends on the warranty terms set by the supplier or manufacturer. Many warranties require approved lubricants and parts, documented service at stated intervals and qualified technicians. Agree in writing before handover what records are needed, who may carry out maintenance, and how parts and oil will be documented so that warranty cover is not put at risk.
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.