Piston, Large - Pressure Reduction Valve, Pneumatic System - Yak 52/Yak 18T
Pressure Relief Valve replacement piston.
When system air pressure in your Yak drops overnight, one of the usual suspects is the PRV piston.
A healthy piston seal and spring combination inside your Pressure Relief Valve is indicated by that staccato AK 47 machine gun noise when the system blows off.
Once you get a building quiet hiss instead, ending in a dramatic blow off, the rubber face on your PRV piston will be starting to show a permanent ring-shaped indentation.
Still functional, but in midlife.
5 years seems to be a predictable lifespan.
Note there are two sizes of PRV piston so be sure to order the correct one for your Yak. If your Yak has 2 or more seats ( Yak 52, Yak 18-T) order this larger one which has a saddle on the outside diameter.
If your machine has one occupant ( Yak 50, 55) order the smaller straight sided body piston here.
Pneumatic system pressure is raised by advancing the hex nut on the PRV thereby compressing a Spring on the backside of the piston. You’re raising the system air pressure required to unseat the seal.
Put another way, that hex nut / spring combination is bearing down 24/7 on the unfortunate little slug of rubber captured in the face of this piston, with hot oily compressed air entering the mix - to make its life just that tiny bit more unbearable.
It takes a special kind of rubber to do the job.
We tested Russian samples for Shore hardness then selected the correct compound and thickness. These rubber slugs are laser cut to create a one-trip fit into the conical recess on the face of the piston. As you may already know, at the end of their lives they’re difficult to dig out.
We use new Brass bodies and dress the all-important face before you get them - but there’s one more critical step to PRV piston replacement Zen that you should observe too.
You’ll have depressurized the Pneumatic system first to remove the old piston ( Fish the spring out too, while your there just to confirm it’s not broken). Install the new piston, spring & Hex nut and compress it to roughly the same number of turns it took to remove it...
THEN LEAVE IT ALONE FOR TWO HOURS without pressurizing the air system.
Pre-seating the rubber seal like this will maximize its life.
After 2 hours, refill with air as normal and adjust the hex cap to give the setting on the cockpit Air pressure gauges that you are used to, always remembering to safety wire the cap once you are done.
These piston/rubber seal assemblies have been tested to perform reliably.
As usual, your satisfaction is guaranteed
Neither of these product are suitable for Nanchang CJ-6