Ever think back to the scorching summers of your childhood, when your dad would cook an egg on the hood of a rusty muscle car just to prove it could be done? How you stood there in complete awe as that lockjaw scramble just sizzled away and you just kept wondering if today was finally the day it would be hot enough to plug the A/C in? Well I’m going to be real upfront with you right now, as nostalgic as this memory feels, if your fire pump gets hot enough to cook an egg on it, you’re in for a very, very bad day.
Casing Relief Valve. Automatic Relief Valve. Cla-Val. Kunkle. CRV. These are all names that get used for what NFPA 20 (Fire Pumps) refers to as a “Recirculating Relief Valve”. The purpose of this bad boy is to allow enough water to flow through the housing of a running fire pump to keep it cool, with no water being discharged down stream. Put simply: Set and working properly, this valve stops the fire pump from melting its own packings, bearings, and housing down around itself, which is kind of important.
These valves ARE adjustable. Different manufacturer’s valves look different, but generally they all follow the same principle. There should be a cap on the top of it. Sometimes these are plastic. Sometimes these are brass. Sometimes these are sacrificed to the sprinkler gods, never to be seen again. Under the cap will be an adjustment screw and a lock nut. The screw puts tension on a spring. Tighten the screw for less water. Loosen it for more water flow. This is the same premise as air maintenance devices and pressure relief valves. It’s almost like there’s a theme here. But here is the most important part about adjusting the recirculating relief valve… NEVER adjust them without the pump running. They only operate when the pump is running. If you adjust them willy nilly without the pump running, you wont know if the pump will overheat the next time it runs. It’s better to flood a drain than to melt a pump.