Pressure relief valve

[jwcoop]

I'm looking for a wet reservoir pressure relief valve for a 1984 M923. Any ideas? Thanks.

 

[Suprman]

With the ABS mod they usually move the safety to the air dryer. I know Napa and Fleetpride (I prefer Fleetpride) have valves at 150 or 160 psi. I dont believe they are the exact thread size you need but Homedepot or your local plumbing supply shop should have the stuff to adapt one to work
Will

 

[doghead]

I would look up the part in question, in the parts technical manual.

Then I would google the part number, to find the manufacturer, and a source.

Another simple method would be to call any of the MV businesses that advertise on our site, and ask if they have the part.

As always, information is helpful.

 

[MyothersanM1]

See part number 19.

NSN 4820011147543
CAGEC/PN 19207 11669104



Hope this helps.

 

[doghead]

So, with that info, a google search and click on the parttarget result and I get this.

http://www.parttarget.com/4820-01-114-7543_4820011147543_279505.html

Scroll down for the bendix and haldex part numbers.

 

[MyothersanM1]

Haldex PN comes up with this...

http://www.class8truckparts.com/Haldex-Midland-Regulating-Valve-KN31000/dp/B002HURU3Q

 

[jwcoop]

Thanks everyone, especially doghead. I'm new at this. My next project is to try to figure out why the wipers won't work.

 

[Suprman]

Does the horn work? The wipers and horn should have air supply around 70psi in the tanks. If you have 80+ psi in your tanks and the wipers and horn are not getting air supply chances are you have a bad pressure protective valve. If your air safety valve is venting to atmosphere and not allowing you to build enough pressure to open the ppv (70psi) then replace it and see what happens. If your ppv is bad and does not open and you just plug up the air safety valve you will build too much pressure and something will blow. The governor is past the ppv it cannot regulate air pressure unless the ppv functions properly.

 

[Floridianson]

With the ABS mod they usually move the safety to the air dryer.

Hay I found mine on M931A1 with ABS on wet the wet tank. It is on the end of the tank almost at the frame rail. ( hard to see ) Mine saftey was popping off yesterday and I tryed to tap on the Pressure protection valve no luck. I cut the safty wire and started to take off the cap and with 1/8 of a turn it released and started to work. I ordered a new one today and will replace it as soon as it gets here. I would never say it is ok to remove the guts out of the Pressure protection valve but one would think if the truck was just needing to be moved offroad the guts could be taken out and cap installed to get out of a jam.

Sorry had to correct

 

[KWDriver]

I think I may have same thing. I made a (more abrupt than normal) stop in my M931A2 and about a min later my low air warning tone and light came on. I limped it another mile until I was able to park it. It appeared to be on the right side, behind the frame, aft of the right fuel tank, trailing edge of air tank between the air line and tank. It appeared to have a button popped on top of it, but i was unable to press back in. I haven't checked the button or the truck. Was 1130pm..parked and walked away.

 

[PapaPumpSD]

Does the horn work? The wipers and horn should have air supply around 70psi in the tanks. If you have 80+ psi in your tanks and the wipers and horn are not getting air supply chances are you have a bad pressure protective valve. If your air safety valve is venting to atmosphere and not allowing you to build enough pressure to open the ppv (70psi) then replace it and see what happens. If your ppv is bad and does not open and you just plug up the air safety valve you will build too much pressure and something will blow. The governor is past the ppv it cannot regulate air pressure unless the ppv functions properly.

I'm in the technical manuals and there are a multitude of "relief valves" (see photo w/red circles). Are these the valves I should be looking at?

My M925A2 has the exact problem descibed by Suprman. The pressure on Primary & Secondary gauges goes beyond 120psi and hits 150psi at which point the truck blows off somewhere near the Haldex unit (maybe it is the Haldex unit blowing off?). This always happens (the air problem) and then our windshield wipers and horn do not work. We already installed a new air governor (under the hood just below the passenger windshield) and a new Haldex PURest unit.

Any help on which parts I should consider replacing (relief valve or multiple valves?) and part numbers would be greatly appreciated.

Note: Truck has been upgraded to ABS.

 

[Suprman]

Bad pressure protective valve its stuck closed. Its by the tanks has a knob on it. Replace that.

 

[PapaPumpSD]

Bad pressure protective valve its stuck closed. Its by the tanks has a knob on it. Replace that.

Suprman, thank you! I'm not a mechanic so any further guidance you can share is appreciated. Below I've pasted a couple of tech diagram images. Is this the "pressure protective valve" I should replace? If so, do I search Ebay for the NSN or is this a NAPA item by chance?





Thank you,

Brent

 

[Floridianson]

Pressure protection valve has two fittings air in and air out easy to figure out. Pressure pop off has no out line it just pops off if pressure goes over set limit. Both can be found on Jbay or truck parts place. I have found the PPV as low as 10 bucks.

 

[PapaPumpSD]

Pressure protection valve has two fittings air in and air out easy to figure out. Pressure pop off has no out line it just pops off if pressure goes over set limit. Both can be found on Jbay or truck parts place. I have found the PPV as low as 10 bucks.

Do I need to purchase both of those items you've listed in the photos? How do I find the part numbers for those items? I need to be sure they'll fit my M925A2.

Thanks!

 

[Floridianson]

I don't know what valve you need I just jumped in with that info. The PPV is set for 60lbs on the military if I remember right but a 70 lbs will work just fine. Most pop off are around 125/130 if I remember. Just figure what one you need and get it on line or truck parts place no part # needed they know what you are doing.
There are 2 of them PPV-PR-65lbs on Jbay right now for 24 bucks.

 

[Swamp Donkey]

Pop-off valve should be 150 psi.

 

[Floridianson]

Post #8 suprman told us how to tell if the PPV valve is bad.

 

[Suprman]

They all go bad anytime I get a truck I swap that and the air dryer. Its inexpensive peace of mind.

 

[PapaPumpSD]

Suprman, thank you! I'm not a mechanic so any further guidance you can share is appreciated. Below I've pasted a couple of tech diagram images. Is this the "pressure protective valve" I should replace? If so, do I search Ebay for the NSN or is this a NAPA item by chance?

View attachment 622776

View attachment 622775

Thank you,

Brent

Can someone please confirm if the red circled part is the PPV that I should replace?