Question:
I am working on a 4” Wilkins reduced pressure principle assembly. The model number is 375A. Can you tell me how this model is different from the 375? Can you also explain how to change out the check valve discs?
Mark:
The difference between the 4” Wilkins model 375A and 375 is the end connections on the device body. The model 375 is the original version and the body style uses an inlet and outlet connection that is flanged. This assembly will use a standard flanged by flanged shut off valve. The 375A body style has grooved end connections on the device body. The shut off valves for this model are attached to the body with a grooved coupler. The internal parts and repair procedures are the same for the 4” 375 and 375A models. No special tools are needed to repair this assembly.
Doug:
The 375 series has a single access cover. The cover is secured by a grooved coupling and there is no spring load. This assembly has check valves that are modular in design and are sometimes referred to as “compound checks.” The springs are contained and the check valve modules are secured by retainers and o-ring sealed into the device body. Note: The first check must be removed before the second check can be removed. It is possible to change the check rubber for the first check without removing it from the body, but to properly inspect the entire check, it must be removed from the body. You will notice that the first check has a plastic ring retainer. The tabs for the retainer are exposed at the 12 o’clock position. Simply pinch the tabs together, push down, and then pull downstream. The check can now be removed by pulling it straight out of the body.
Mark:
With the first check out, the second check can now be removed. The second check is secured by two separate spring-loaded plate retainers. They are located at the 12 and 6 o’clock positions. Pinch the sides of the spring together and rotate the plates out of the body groove, one at a time. The second check can now be removed by pulling it straight out of the body. Once the modules have been removed, they must be disassembled to access the check discs. Note that the spring tension is contained when the check is taken apart. Be cautious to not remove any hardware from the spring side of the module. The downstream side of the check will have four hex head bolts that must be removed. Once they have been removed, the retainer can be separated from the module and the disc is free to be replaced. It is also important to inspect the check valve seat. The seat is an integral part of the check module, so if there is any damage, the entire check must be replaced.
Doug:
Once service has been completed, reassemble each module in reverse order. As you reinstall the checks, make sure the rollers are positioned at 3 and 9 o’clock so that they will not get in the way of the retainers. Here are some tips on reinstalling the retainers: Install the plastic retainer by inserting one end into the body groove and then sliding your hand around the face of the retainer, pushing it into the groove. It will snap into place when it is fully seated. Install each wire retainer into the body groove one at a time. Pinch the sides of the spring together and rotate the plates into the groove.
