Pressure relief valve

[Floridianson]

That looks like PPV but the # 20 fitting should not be there. The PPV comes off the wet tank and piped to the other tanks. You can not always use the TM' for the pictures as could have mistakes.

 

[Swamp Donkey]

That looks like PPV but the # 20 fitting should not be there. The PPV comes off the wet tank and piped to the other tanks. You can not always use the TM' for the pictures as could have mistakes.

My truck is plumbed exactly like that, including the Tee.

 

[Floridianson]

But should it not show the line out of the PPV. It shows it at a dead end of the block. It has been awhile since I have seen it.

 

[Swamp Donkey]

Double post

 

[Swamp Donkey]

The line coming off the PPV most likely ended up in another diagram. While the picture makes it appear to be deadended, there is a line leaving the PPV on my truck.

 

[PapaPumpSD]

Ok guys, here's what I ended up doing and the result:

1) I replaced the check valve that is found by following the Haldex line leading to the 1st air tank.
Part Number: KN23000 (Napa: $23.00). This valve was stuck shut and the inside was very corroded. It definitely needed replacement.
2) I fired the truck up and it went over 120psi and started to blow off but it sounded different that when it blew off at 150psi w/the old valve.
3) I banged on the safety valve (ST-3 valve as shown in the image) and then restarted the truck and it never went over 120psi and did not blow off.
4) The horn and windshield wipers did not work at all today, reglardless of the new check valve.
5) I drove the truck forward & backward 10 feet but when the truck was at 120psi & I used the brake, it seemed to continuously bleed off and I could hear it, like it was coming from the intake stack. It was a not a big wooshing sound, rather a dull "exhale". In fact, starting at 120psi and braking continuously, the primary pressure ended at 50 psi (10 feet of braking distance).





Thoughts?

Thank you,

Brent

 

[Swamp Donkey]

1. Replace PPV as has been suggested. Given all the symptoms you've posted in this thread it is not working right. Troubleshooting anything further until this is done won't get you very far.

2. Replacing the PPV should stop the relief valve from opening. If it purges, and you're below 150 psi, then replace the relief valve. The spring inside can get weak or break over time.

3. The exhausting into the intake stack sounds like a ruptured brake chamber diaphram. Since it only happens during brake application it's most likely a service brake diaphram. Run shop air through the emergency gladhand and have somebody work the brakes while you determine which one it is. The brake chambers vent to the intake stack.

 

[MtnSnow]

Ok guys, here's what I ended up doing and the result:
5) I drove the truck forward & backward 10 feet but when the truck was at 120psi & I used the brake, it seemed to continuously bleed off and I could hear it, like it was coming from the intake stack. It was a not a big wooshing sound, rather a dull "exhale". In fact, starting at 120psi and braking continuously, the primary pressure ended at 50 psi (10 feet of braking distance).
Thoughts?

Thank you,

Brent

Your LQ2 valve has broken. It is the valve that is located at the front of the truck just ahead of the axle on a vertical plate. Looks like this

 

[PapaPumpSD]

Your LQ2 valve has broken. It is the valve that is located at the front of the truck just ahead of the axle on a vertical plate. Looks like this View attachment 623061

Thanks for the help.

Here's my approach to finding parts locally. For this item, the "LQ2 valve", which, per the tech manual, is a "valve, linear, direct" (tech manual keyword "quick release valve"), there are two different valves:
1) NSN 4820007287467; Part Number:278614; VALVE, LINEAR, DIRECT (figure 256-1) <--2 of these
2) NSN 4820008572737; Part Number:11602155; VALVE, LINEAR, DIRECT (figure 256-1) <--1 of these valves

I searched Napa online for the PART NUMBERS (not the NSN) and I get parts. For the items above, for PN 11602155, it's Napa part MBI 288251X. Will this approach get me the proper parts?

How do I know which valve part number to get? Diagram below.



Thanks!





Brent

 

[PapaPumpSD]

We replaced the PPV and 150 psi ST-3 safety valve and adjusted the governor (located under the passenger-side windshield, under the hood). The pressure holds fine at 120psi primary tank now.