Question about the air tanks

[gemini25]

Hallo,

I have a strange problem and wanted to know, if this is normal, or what could be the issue.
For the tests, all air tanks are filled up.
1) If I drain the primary air tank, the secondary air tank keeps it's air (I guess, this is how it should be).
2) If I drain the secondary air tank, the primary air tank loses pressure (I guess, this isn't normal).
In the second case, has anybody an idea, what could cause the problem.

Thank you
Theo
(M1078A1 - 2003)

 

[Ronmar]

There is a check valve at the inlet of the primary and secondary air tanks(where wet tank connects to each tank). These checks are to keep the systems separate, so one failure doesn’t kill the other system. It sounds as if your primary inlet check is leaking...

The check valves that are used, screw together, and you can take them apart to clean and inspect. Could be something in the valve or it may be corroded/pitted and needs to be replaced...

 

[gemini25]

Thank you, I will check it

 

[gemini25]

So, I had a close look at the two one way valves. Strange think, in one of the valves wasn‘t a spring.
Just to get sure, this is the problem, I switched the valves.
But the problem remains the same. Anyway, I will get to two valves and will see what happens.

 

[Ronmar]

So, I had a close look at the two one way valves. Strange think, in one of the valves wasn‘t a spring.
Just to get sure, this is the problem, I switched the valves.
But the problem remains the same. Anyway, I will get to two valves and will see what happens.

Well they are both supposed to have springs, but if you swapped the complete valves and the issue didn’t change, that indicates that those valves are not the issue.
if you leave both tanks full do they hold pressure? There are also three 2way check valves that can draw air from either tank which could be leaking past once there is a difference in pressure between the pri and sec tanks...

 

[gemini25]

If both tanks are full, yes, they hold the pressure. Or let's say, they keep the pressure for 24 hours.

Thanks for the hint. I will have this week a close look, didn't have time the weekend. I will post the results.

 

[Ronmar]

If both tanks are full, yes, they hold the pressure. Or let's say, they keep the pressure for 24 hours.

Thanks for the hint. I will have this week a close look, didn't have time the weekend. I will post the results.

1 of the valves is located under the drivers dash where the pressure gauge sensors are located. One is at the service tanks and it feeds a small line over to supply air to the valve that controls the cab lift hydraulic pump. The third is I believe back on the crossmember over the rear axle(drivers side).

If you drain the one tank, you might be able to hear air leaking thru the 2way with a mechanics stethoscope... Maybe...

 

[gemini25]

Thanks a lot for your help. I will have a close look this week.