Question:
I am servicing a 4” Wilkins double check detector assembly. The model number is 350ADA. Can you tell me about this assembly and explain how to change out the check valve discs of the large assembly?
Mark:
The Wilkins model 350ADA started production in 2004 and is a double check detector assembly. This model is normally used on fire suppression systems. The body is made of epoxy coated ductile iron and 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 350ADA also comes standard with a type 1 metered bypass assembly. The device used on the bypass is a ¾” 950XLD. No special tools are needed to repair the mainline assembly.
Doug:
The mainline (larger) assembly of the 350ADA 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 completely 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, but to properly inspect, the entire check 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 in 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:
Now that the first check is out, we can remove the second check. The second check is secured by two separate spring-loaded plate retainers, which are located at the 12 and six 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.
Now that the modules have been removed, we must disassemble them 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 need to be removed. Once they have been removed, you can separate the disc retainer from the module and the disc is free to be replaced. It is also important to inspect the 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 the check disc has been replaced, simply reassemble each module in reverse order. As you reinstall the checks into the body, make sure the rollers are positioned at three and nine o’clock so that they will not get in the way of the retainers.
Here are some tips on reinstalling the retainers: For check #1, 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 as you go. It will snap into place when it is fully seated. For check #2, install each wire retainer, one at a time, into the body groove. Pinch the sides of the spring together and rotate the plates into the body groove.
