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jrburch1946 · 01-24-2019, 12:55 PM

When I drain wet tank no change in sys 1 or sys 2 pressure, when I drain sys 1 tank pressure drops in both tanks. drain sys. 2 tank both sys. drop. Appears tank check valves are both working, however sys. are working as one ??? Please help!!

1997 HR 40 WDS on Spartan MM chassis,c8.3 cummins, Allison 3060

twinboat · 01-24-2019, 01:17 PM

There should be a double check valve between the wet tank and both tank 1 and 2.

It may be stuck open.

BRex45 · 01-24-2019, 01:20 PM

It's quite possible, but not always, the check valve(s) are stuck (rusted) I would also check to make sure the gauges were plumbed correctly.
When you apply the brakes several times do the air pressure gauges drop at the same rate?

Keep us posted on your findings.

jrburch1946 · 01-24-2019, 01:30 PM

yes both gauges drop the same with brake application. Apprears ck valves that keep air in each tank are working. If stuck open pressure would drop when wet tank is drained. So connection of systems must be elsewhere???

barmcd · 01-24-2019, 02:16 PM

I think you have a check valve that isn't stopping air flow between the two dry tanks. The way yours is working, a leak in one tank would lead to a total loss of air to the coach.

My front tank is split in half, one side wet and the other side dry. There has to be a check valve between the two dry tanks to keep air from leaking out of the system if one half develops a leak. Make sense?

twinboat · 01-24-2019, 05:25 PM

Its been years since my training on the 121 system but I believe the outputs of both tanks go to a double check valve.

If one system drops rapidly, a shuttle in the valve shifts over to block the flow so you don't loose the other.

I circled a valve marked DC-4. It ties the tanks together if not functioning correctly.
Attachment 232991

jrburch1946 · 01-28-2019, 06:15 PM

Good news Problem resolved its self!!! I filled coach to 120#, drained each tank to 0# repeated 3 times without change on 4th attempt each tank responded correctly, losing pressure independently!!!!! TX Ron

rag_ftw · 01-30-2019, 08:50 PM

Quote:

Originally Posted by jrburch1946

Good news Problem resolved its self!!!...TX Ron

Odds are it's a temporary "fix". Now would be a good time to purchase a new shuttle valve.

OldHatt45 · 01-31-2019, 08:32 AM

jrburch1946,
Sounds to me like you may have a basic problem with the air system.
Water (or oil) in your air system.
When was the last time you changed the Desiccant Filter in your air system???
If the Desiccant Filter is not doing its job, it will allow moisture (water or oil) into the air tanks. With fluid in the air tanks, you run into problems such as rust, etc. happening and causing valves to stick, air lines to get clogged, etc.

Drew
2003 Travel Supreme 40DS02

Ray,IN · 01-31-2019, 02:07 PM

Spartan air tank system pdf clearly shows the wet tank on the left portion of the tank.
(for some reason the drawing is upside down, use the rotate feature in the toolbar to get right side up.)

rag_ftw · 01-31-2019, 02:15 PM

Quote:

Originally Posted by OldHatt45

jrburch1946,
Sounds to me like you may have a basic problem with the air system.
Water (or oil) in your air system.
When was the last time you changed the Desiccant Filter in your air system???
If the Desiccant Filter is not doing its job, it will allow moisture (water or oil) into the air tanks. With fluid in the air tanks, you run into problems such as rust, etc. happening and causing valves to stick, air lines to get clogged, etc.

Drew
2003 Travel Supreme 40DS02

Shuttle valve failure is pretty common on our older coaches. I had to replace mine last summer as I couldn't get the parking brake to release. I believe it was around $40.00 at a truck supply house. It is a common part used on many different vehicles. Part number is visible in photo.

Routinely changing the desiccant filter is also a very good practice.

jrburch1946 · 02-01-2019, 08:48 PM

I would like to find root cause of problem, so thanks for info. Is what you are referring to as shuttle valve the double check valve located at manifolds where pressure switches and air pressure gauge get air supply? Mine is Parker ar00002 and appears good.