Wilkins 450DA: How To Repair
I am working on a 4” Wilkins 450DA. Can you tell me how to remove the check valves and replace the check valve discs?
The Wilkins 450DA is a double check detector assembly. The 450DA series is unique because it is designed to be used in the “N” shaped configuration. This unit has a single access cover. The cover is secured by a grooved coupling and there is no spring load. Both check valves 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. No special tools are needed to repair this assembly.
It is important to note that the first check must be removed before the second check can be removed. It is also 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. With the access cover removed, 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 valve can now be removed by pulling it straight out of the body.
With the first check out of the Wilkins 450DA, we can remove the second check. 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. Now that the modules have been removed, we must disassemble them to access the check discs. Note that the spring tension is contained while 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 4 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 important to inspect the seat, which is an integral part of the check module. If there is any damage, then the entire check must be replaced.
Once service has been completed, simply reassemble each module in reverse order. Remember to reinstall the 2nd check before the first check. As you reinstall the checks into the body 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 installing 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 as you go. 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 body groove. They will snap into place when they are fully seated.