DISCHARGE CHECK VALVE OF COMPRESSOR

DISCHARGE CHECK VALVES



The installation of a check valve on the discharge of Turbocor compressor is mandatory to prevent the compressor rotating backwards on shutdown as well as pressure from the condenser flowing backward through the compressor to the evaporator when the compressor is  shut down.

While there is little to guide the service technician regarding the maintenance/ replacement of this item, it is the experience/ recommendation of the author that anytime the Turbocor compressor operates in surge for any length of time, or has a failure due to a front radial bearing issue (which probably has been caused by surge), as a minimum, the discharge check valve should be inspected for possible damage and replaced as appropriate.

There are two types of check valves commonly used with the Turbocor compressor.  One is a wafer type, swing check valve.  The other is a plunger type combination check valve/ isolation valve.

The wafer type, swing check valve uses a ¨flapper¨ type disc with a spring to assist it in closing.  It can be mounted with the valve opening horizontally or opening in an ¨up¨  position.  This type of valve can´t be mounted such that it opens in a ¨down¨ orientation.  Normally, this valve is used in conjunction with a ¨ball¨ valve for isolation purposes. 

The swing check valve has advantages in that it takes up less space, is less expensive and is easier to replace  when replacement is necessary.

The disadvantage of the swing check valve is that when it closes, it does so rather forcefully and seals with a metal on metal seal.  While there is no proof of this, the observation of the author is that when the swing check valve closes, it creates a more abrupt disruption of the gas flow and possibly is more likely to cause a displacement of the compressor shaft which could lead to the shaft coming in contact with the touchdown bearing (and possible failure of the touchdown bearing).  Additionally, the author has experienced several instances where the ¨flapper¨ of the swing check valve fractured, causing parts of the ¨flapper¨ to be sucked back into the compressor, damaging the compressor rotors.

The plunger type combination check valve/ isolation valve, there is a substantial Teflon seal that takes the ¨impact¨ of the closing force of the valve, plus the inertia of the plunger is much less than that of the swing check valve.  The valve takes up more space in the installation, but does not require a separate isolation valve.  However, in order to inspect the valve, the refrigerant charge must be removed from the condenser.  There is a rebuild kit available for these valves.

In the opinion of the author, these valves are much less subject to a ¨catastrophic¨ failure that could also lead to compressor failure. On the other hand, damage to the valve could impair its ability to close properly, which would allow reverse refrigerant flow through the compressor and possible compressor damage. However, as with the swing check valve, in the case where the compressor has been subject to repeated episodes of surge or there has been a compressor failure due to front radial bearing issues, this valve should be torn down and inspected, as a minimum.