Compressors

Diaphragm Compressors

In a diaphragm compressor, oscillating hydraulic pressure on one side of the diaphragm causes it to deflect inside a chamber, compressing the gas on its other side. Inlet and outlet valves allow low pressure gas to enter the compressor, and the pressurised gas to be discharged to the system. The oscillating pressure is generated by a piston moving in a cylinder.

In more detail (refer to Figure 1):
The crankcase (A) of the compressor is essentially a hydraulic pump. The piston (1) moves in the cylinder (2) and pulses the hydraulic fluid in the head (B) producing an oscillating movement of the diaphragm group (8).

The diaphragm group consists of three diaphragms clamped and sealed at the periphery between the gas plate and orifice plate.

The orifice or channel plate (4) has the role of distributing the hydraulic fluid uniformly under the diaphragm and the gas plate (5) contains the suction (6) and discharge (7) check-valves.
 
These two plates are specially contoured on their internal faces and their assembly forms the compression chamber. Their profile is carefully designed so as to minimize the stresses in the diaphragm.

A piston pump called the compensating pump works via an eccentric mounted on the crankshaft. At each stroke of the piston a surplus of hydraulic fluid is injected into the oil chamber to compensate for any leakage past the piston and to assure the diaphragm (8) makes full contact with the gas plate (5).

The clearance volume is thereby reduced to a minimum.

The excess hydraulic fluid introduced by the compensating pump escapes via an adjustable relief valve called the pressure limiter (3) and returns to the sump.

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