ARI RP-500: How To Repair

Monday September 14, 2020

I need to work on a ¾” ARI RP-500. Can you guys give me an overview of this assembly and any tips that may help me if I need to make a repair?


The ARI RP-500 is a reduced pressure principle assembly. This unit is relatively new to the US market. They are produced in 3/4-inch – 2-inch sizes. The body is made of a black composite plastic material. The inlet and outlet shut off valves and test cocks are made of brass. All the internal components can be removed through a single access cover. The check valves for the RP-500 are modular in design and are held in place with a retainer. No special tools are required to complete the repair of this assembly. The ARI DC-500 is a double check valve assembly (DCA) and is very similar to the RP-500. The check valve repair procedures are identical so we will go over the repair for both assemblies.


The access cover is sealed by the relief valve diaphragm and is secured with six Philips head screws. There is a slight spring load on the cover, so be sure to keep pressure on it as you remove the screws.

Once the cover has been removed, the relief valve stem assembly and spring are free and can be inspected. To replace the RV diaphragm, remove the screw at the top of the RV stem.

ARI DC-500 Cover Removal

Once the screw is removed, the top plate is free and the diaphragm can be inspected or changed. There is an o-ring located on the RV stem under the bottom diaphragm plate. Simply slide the bottom plate back to expose the o-ring. The relief valve disc is located at the bottom of the stem assembly and is held in place by the stem fin guide. The rubber disc must be pulled out from around the fin guide.

Please note that the stem fin guide is not removable, so be careful not to damage it when removing the rubber disc. The relief valve seat is o-ring sealed and made of white plastic. The RV seat is located in the bottom of the device body and is pushed into the device body. The seat can be pushed out from the underside of the assembly.

ARI DC-500 Stem Guide


The check valve modules for the ARI RP-500 and ARI DC-500 are made of a white plastic and the springs are contained. The check valves modules are o-ring sealed into the body and are held in place by a retainer. The check retainer is white plastic and will slide straight up and out of the device body. The check valves can be removed by first using a screwdriver to pry them from the body and then sliding them toward the access hole. Once the check modules have been removed, you can examine or replace the o-ring along the outside of the check module. The check modules are not designed to be disassembled any further. If there is a problem with the module, it must be replaced.


At this point we can reinstall the checks by sliding them back into the body. The check retainer should slide into place very easily. If it does not, make sure the checks are fully seated into the body. The RV stem will insert through the hole in the retainer. The RV spring will rest on top of the check retainer. Before you reinstall the cover, be sure to examine your sensing line o-ring, which is located inside the sensing line passage of the body. Finally, remember that the diaphragm is what seals the access cover, so make sure that the ridge on the diaphragm lines up with the groove on the body before you tighten the cover screws.