Sight Glass And Moisture Indicator

Sight Glass And Moisture Indicator 

A combination sight glass and moisture indicator is essential for easy field maintenance on any system, and is required on any field installed system unless some other means of checking the refrigerant charge is provided.

A sight glass in a convenient means of determining the refrigerant charge, showing bubbles when there is insufficient charge, and a solid clear glass when there is sufficient charge. however, the operator should bear in mind that under some circumstances even when the receiver outlet has a liquid seal, bubbles or flash gas may show in the sight glass. This may be due to a restriction or excessive presure drop in the receiver outlet valve, a partially plugged drier or strainer, or other restriction in the liquid line ahead of the sight glass. If the expansion valve feed is erratic or surging, the increased flow when the expansion valve is wide open can create sufficient pressure drop to cause flashing at the receiver outlet.

Another source of flashing in the sight glass may be rapid fluctuations in compressor discharge pressure. For example, in a temperature controlled room, the sudden opening of shutters or the cyclinng of a fan can easuly cause a reduction in the condensing temperature of 10 º F. to 15 º F. Any liquid in the receiver may then be at a temperature higher than the saturated temperature equivalent to the lower condensing pressure, and flashing will continue until the system has stabilized at the new condensing temperature.

While the sight glass can be a valuable aid in servicing a refrigeration or air conditioning system, a more positive liquid indicator is desirable, and the system performance must be carefully analyzed before placing full reliance on the sight glass as a positive indicator of the system charge.