Oil Pumps - Suction Gas-Cooled Compressors; Oil Pressure; Oil Circulation - Emerson Copeland Discus Series Application Manuallines

K & L compressor oil circulation
The oil returning from the evaporator reaches the crankcase via an oil separator chamber behind
the suction shut-off valve through a small connecting bore. Due to this connecting bore the
crankcase pressure will be decreased slowly when the compressor starts. Thus the foaming of
the oil and refrigerant mixture will be reduced.
Figure 3: K & L compressors lubrication
2.6.8 Oil pumps – Suction gas-cooled compressors
The oil pumps used for standard and Discus compressors are independent of their rotating
direction. They are designed to accommodate fittings for an OPS1, OPS2, SENTRONIC oil
safety system or a standard oil pressure switch.

2.6.9 Oil pressure

Normal oil pressure is between 1.05 and 4.2 bar higher than crankcase pressure. Net oil
pressure can be read by connecting two pressure gauges to the compressor and comparing the
readings. One gauge should be connected to the oil pump. The second gauge should be
connected to the crankcase (T-fitting instead of plug on the compressor crankcase) or the
suction service valve.
During irregular operating conditions, eg, a blockage of the suction filter, the pressure measured
at the suction shut-off valve of the compressor may differ widely from that measured at the
crankcase therefore pressure drops have to be avoided.

2.6.10 Oil circulation

Oil returns with the suction gases through a suction strainer and separates in the motor chamber
reaching the crankcase by way of a pressure relief valve in the partition between motor housing
and crankcase. This relief valve closes on compressor start-up due to the pressure difference
arising between motor side and crankcase, thus slowing down pressure decrease in the
crankcase over a certain period of time. It reduces the foaming of the oil/refrigerant mixture that
would occur if the pressure decreased rapidly.
The valve does not reopen until the pressure has been equalized by means of a crankcase
ventilating valve. This second valve connects the crankcase and suction side cylinder head. It
reduces the pressure difference by means of a very small bore in the plate of the valve so slowly
that oil foams less and only limited oil/refrigerant foam is transferred to the oil pump.
10 D6.3.4/0715-0716/E