Liquid overfeed systems are known for providing effective heat transfer and reducing operating expenses. In a liquid overfeed system with a mechanical pump recirculating the refrigerant, the use of hermetic pumps is a growing practice.
A pump is used to circulate refrigerant through the evaporator(s) such that the evaporator surface is used more efficiently, providing better heat transfer.
The two types of mechanical pumps used for liquid overfeed systems are either hermetic or open drive. Hermetic refrigerant pumps reduce the risk of unwanted refrigerant leaks because of their seal-less design.
Open-drive vs. hermetic liquid refrigerant pumpsOpen-drive pumps depend on mechanical seals to minimize refrigerant leakage from around the shaft. The shaft penetrates into the pressurized containment boundary on the pump.
Shaft seals are usually spring assisted and require lubrication systems to prolong seal life and withstand pumping pressures. Also, open-drive pumps have bearings that must be lubricated. Refrigerant pump seals wear out, costing owners in refrigerant, replacement seals, downtime, and potential fines, injury, and product loss.
Open-drive pumps also use conventional motors, which are subject to dirt, moisture, and ice build-up. Often these motors require auxiliary fan cooling and are noisy.
Hermetic pumps do not require a shaft seal because the shaft and the rotor are one assembly that is completely immersed in the pumped refrigerant. A gasketed, stainless steel can encases this assembly, and is connected to the pump housing.
A hermetic pump uses the pumped refrigerant liquid to provide lubrication to the bearings. Because there are no shaft seals, oil level maintenance is eliminated.
Hermetic motors are totally sealed from external dirt, moisture, and ice. They are cooled by the pumped refrigerant and require no auxiliary devices to provide heat removal. The pump motor provides a secondary containment shell to further protect against refrigerant leakage.
Seal life is three months to several years on an open-type pump. Changing seals requires opening the pump to the atmosphere. Refrigerant leakage indicates a need for maintenance.
With no shaft seals to wear out, costs are minimized in a hermetic pump. Unless a hermetic pump is very dirty, the pump repair interval exceeds five years, at which time bearings may need replacement. Noise or vibration will indicate a need for maintenance.
The solution for an efficient liquid overfeed system with an effective defense against refrigerant leakage can be found in the hermetic liquid refrigerant pump.
Hansen Technologies’ hermetic pumps are compatible with ammonia, R-22, and R-134a, as well as a range of non-corrosive, highly volatile liquids. For more information, contact the company at 6827 High Grove Blvd., Burr Ridge, Ill. 60521; 800-426-7368; 630-325-1572 (fax); firstname.lastname@example.org (e-mail); or www.hantech.com (website).