Suction Line Accumulators

Suction Line Accumulators

If liquid refrigerant is allowed to flod through a refrigeration or air conditioning system ans return to the compressor before being evaporated, it may cause damage to the compressor due to liquid slugging, loss of oil from the crankcase, or bearing washout. To protect against this condition on systems vulnerable to liquid damage a suction accumulator may be necessary.

The accumulator´s funtion is to intercept liquid refrigerant before it can reach the compressor valves or crankcase. It should be located in the cuction line near the compressor, and if a reversing valve is used in the system, the accumulator must be located between the reversing valve and the compressor. Provisions for positive oil return to the crankcase must be provided, but a direct gravity flow which will allow liquid refrigerant to drain to the crankcase during shut-down periods must be avoided. The liquid refrigerant must be metered back to the compressor during operation at a controlled rate to avoid damage to the compressor.

Some systems, because of their design, will periodically flood the compressor with liquid refrigerant. Typically, this can occur on heat pumps at the time the cycle is switched from cooling to heating, or from heating to cooling. The coil which has been serving as the condenser ir partially filled with liquid refrigerant, and when suddenly exposed to suction pressure, the liquid is dumped into the suction line. On heat pumps equipped with expansion valves, there may be further flooding due to the inability of the expansion valve to effectively control refrigerant feed for a short period after the cycle change until the system operation is again stabilized.

A similar situation can accur during defrost cycles. With hot gas defrost, when the defrost cycles is initiated, the sudden introduction of high pressure gas into the evaporator may force the liquid refrigerant in the evaporator into the suction line. If the defrost cycle is such that the evaporator can fill with condensed liquid during defrost, or on systems utilizing electric defrost without a pumpdown cycle, an equally dangerous situation may exist at the termination of the defrost cycle.

On systems with a large refrigerant charge, or on any system where liquid floodback is likely to accur, a suction line accumulator is strongly recommended. On heat pumps, truck applications, and on any system where liquid slugging can occur during operation, a suction line accumulator is mandatory for compressor protection unless otherwise approved by the copeland application engineering department. The actual refrigerant holding capacity needed for a given accumulator is governed by the requirements of the particular application, and the accumulator should be selected to hold the maximum liquid floodback anticipated.