Richard and Rhonda
12-22-2008, 08:20 PM
You guys will have to forgive me for being such an OCD engineer. It bugs me that the leveling valves seem to be a chronic problem, and there is not a good way to diagnose which one is giving you the problem.
So, I made a little jig to test the valves with. It was pretty simple, although the threads on the valves are 1/2-20 that is really close to 1/4 NPT, so I cheated and used a 1/4 NPT pipe coupling. On the side that mates to the valve, I used a brass washer robbed from an old valve, and used epoxy to seal the 1/4 NPT coupling to the washer. I drilled a hole in the washer to simulate the setup on the manifold distribution block in the coach. so to use the jig I applied air through a regulator, and put a soap bubble over the hole in the washer. I increased the air pressure using the regulator until I saw a bubble form. I called that the leak pressure.
I conducted a little experiment with the help of another. I was sent two old KIP valves that he had, I had two old AV brand valves, and two brand new HWH valves I just bought. My goal was to determine the cause of the chronic failures.
I disassembled all three sets and took some measurements of the springs and valve seats. I also used the jig to determine the pressure at which the valves started to leak by. To be more accurate, I should have used a 12 VDC source and cycled the valves a few times. Maybe next time.
Here are the data:
New/Used Brand Spring Ht Durometer Leak Pressure
New HWH (AV) 0.52 47 100+
New HWH (AV) 0.54 50 100+
Used AV 0.47 49 55
Used Kipp 0.54 35 10
Used Kipp 0.56 34 10
AV Urethane seat 100+
Reworked seat, lapped 70
New valve old seat 70
Old valve, new seat 100+
The experiment seems to indicate that significant deterioration in performance. No wonder we can't keep air in the bus. You can also see that the hardness of the seat, and spring height does not explain the change in leakage. I concluded it had to be degradation of the contact between the valve seat and the valve body.
I had made a new seat for one of the old valves out of same castable urethane I had in the office. First indication is that something like that may work to refurbish the valves, since that reworked valve did achieve near new leak rates. I do not know how long that material would hold up under use
I also tried lapping the valve and valve seat together using finger pressure and a light lapping compound (tootpaste). The lapping raised the leak pressure 15 pounds but did not fix the leak.
I also swapped an used seat into a new body, and a new seat into an old body to determine if the leak was seat or body related. One single data point indicates it's the seat.
It makes sense that the seat would be degraded by air blowing past it. The valve body is brass and the seat seems to be some moderately hard polymer. That was my intial thoughts anyway, but I had to prove it to myself before going to the next step.
I had two goals. One to make a device to be able to test the valves easily. Mission accomplished. Total cost about two dollars. The second was to ultimately be able to recondition the valves to seal in an easy and inexpensive manner. I will have to get some different urethanes to try now. I'll report back later on what I find.
Of course if the valve is not opening, that's a different problem, and requires a new coil. But generally people complain about them leaking.
Guys, don't throw the old ones away, there may be help on the horizon.
So, I made a little jig to test the valves with. It was pretty simple, although the threads on the valves are 1/2-20 that is really close to 1/4 NPT, so I cheated and used a 1/4 NPT pipe coupling. On the side that mates to the valve, I used a brass washer robbed from an old valve, and used epoxy to seal the 1/4 NPT coupling to the washer. I drilled a hole in the washer to simulate the setup on the manifold distribution block in the coach. so to use the jig I applied air through a regulator, and put a soap bubble over the hole in the washer. I increased the air pressure using the regulator until I saw a bubble form. I called that the leak pressure.
I conducted a little experiment with the help of another. I was sent two old KIP valves that he had, I had two old AV brand valves, and two brand new HWH valves I just bought. My goal was to determine the cause of the chronic failures.
I disassembled all three sets and took some measurements of the springs and valve seats. I also used the jig to determine the pressure at which the valves started to leak by. To be more accurate, I should have used a 12 VDC source and cycled the valves a few times. Maybe next time.
Here are the data:
New/Used Brand Spring Ht Durometer Leak Pressure
New HWH (AV) 0.52 47 100+
New HWH (AV) 0.54 50 100+
Used AV 0.47 49 55
Used Kipp 0.54 35 10
Used Kipp 0.56 34 10
AV Urethane seat 100+
Reworked seat, lapped 70
New valve old seat 70
Old valve, new seat 100+
The experiment seems to indicate that significant deterioration in performance. No wonder we can't keep air in the bus. You can also see that the hardness of the seat, and spring height does not explain the change in leakage. I concluded it had to be degradation of the contact between the valve seat and the valve body.
I had made a new seat for one of the old valves out of same castable urethane I had in the office. First indication is that something like that may work to refurbish the valves, since that reworked valve did achieve near new leak rates. I do not know how long that material would hold up under use
I also tried lapping the valve and valve seat together using finger pressure and a light lapping compound (tootpaste). The lapping raised the leak pressure 15 pounds but did not fix the leak.
I also swapped an used seat into a new body, and a new seat into an old body to determine if the leak was seat or body related. One single data point indicates it's the seat.
It makes sense that the seat would be degraded by air blowing past it. The valve body is brass and the seat seems to be some moderately hard polymer. That was my intial thoughts anyway, but I had to prove it to myself before going to the next step.
I had two goals. One to make a device to be able to test the valves easily. Mission accomplished. Total cost about two dollars. The second was to ultimately be able to recondition the valves to seal in an easy and inexpensive manner. I will have to get some different urethanes to try now. I'll report back later on what I find.
Of course if the valve is not opening, that's a different problem, and requires a new coil. But generally people complain about them leaking.
Guys, don't throw the old ones away, there may be help on the horizon.