Spare parts
Unloaders for reciprocating compressors
Pneumatic unloader heads for capacity control via the suction valve – direct-acting or spring-loaded, to fit compressors of different makes, manufactured from a sample or drawing.
How the unloader works
Pneumatic unloader heads for capacity control via the suction valve. Diaphragm unloader with pneumatic actuation, direct acting.
When compressed air is applied to the control air port, the diaphragm plate and spindle move towards the valve and compress the return spring. The spindle moves the unloader finger, which pushes the valve plate off the valve seat and holds it against the guard. As long as control pressure is applied, the suction valve stays open. On the compression stroke the gas drawn in is pushed back into the suction line, so that cylinder end does not deliver and runs unloaded.
For full load the control air is vented. The spring returns spindle and unloader finger to their initial position, and the suction valve works normally again. If the control air fails, the cylinder automatically runs at full load.
Designs
Unloaders (pneumatic unloader heads) open the suction valve and hold it open – the cylinder runs idle and the capacity drops. Two designs:
- Direct acting (air-to-unload): compressed air opens the suction valve; without air, the spring returns to full load.
- Reverse acting (spring-to-unload): without control pressure the spring pushes the suction valve open; pressure is applied for full load.
Mounted with a four-bolt flange on the valve cover; a bore in the housing vents the process gas.
Matching suction valves
For capacity control we also supply the matching suction valves with unloader finger – designed for your compressor and operating point. See suction and discharge valves
What we need for a quotation
- Compressor make, type and nameplate (a photo is enough)
- Photo or drawing of the unloader and the valve cover
- Design: direct-acting or spring-loaded
- Control air pressure
- Quantity
Frequently asked questions
Do you supply original parts?
No. We supply matching unloaders, designed and specified under our own responsibility. Brand names are used for reference only; there is no affiliation with the respective manufacturers.
Can you reproduce an unloader from a sample?
Yes. From a sample or photos with dimensions we reconstruct the unloader and manufacture it – even if it is no longer available.
Do you also supply spare parts for unloaders?
Yes. Diaphragms, return springs and seals are also available individually, from a sample or drawing.
Send us a drawing, photo or nameplate
Send whatever you have – drawing, photo of the sample, nameplate or operating data. We usually reply within 24 hours on working days and prepare a free, non-binding quotation for you.