NickZ
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- Joined
- Oct 31, 2018
- Messages
- 457
I've read several of the PRV threads but this is a little different.
While I am servicing the timing chest of my 71 Roadster, I thought I would check the PRV after I had cleaned up the body, replaced the piston & spring, and shimed it till it rattled. I thought of a simple setup that could test pressure in vs pressure out, but not sure how relevant it is because I used air pressure, not oil in the test. The setup, pictured below, is just a timing cover with the crankshaft port sealed with a cut off rubber muffler mount that I turned down to the right size so it could be circlipped in where the seal normally goes. A pressure gauge is connected to the rocker feed output and air pressure is injected from my compressor into the port where the oil pump output goes.
What I found that surprised me was that at any input pressure, there was always a loss of pressure thru the PRV, roughly 20% even before the piston moved. I double checked this by replacing the spring with a bolt so the piston can't move. With the spring, the valve would relieve more pressure as compressor pressure got above 60 psi, as I would expect a functioning PRV to do.
My question: Is this initial pressure loss, a) a function only of using air pressure, b) also present with normal operation with oil pressure, or c) because my PRV is bad?
For anyone interested, here is what I measured with the compressed air setup:
While I am servicing the timing chest of my 71 Roadster, I thought I would check the PRV after I had cleaned up the body, replaced the piston & spring, and shimed it till it rattled. I thought of a simple setup that could test pressure in vs pressure out, but not sure how relevant it is because I used air pressure, not oil in the test. The setup, pictured below, is just a timing cover with the crankshaft port sealed with a cut off rubber muffler mount that I turned down to the right size so it could be circlipped in where the seal normally goes. A pressure gauge is connected to the rocker feed output and air pressure is injected from my compressor into the port where the oil pump output goes.
What I found that surprised me was that at any input pressure, there was always a loss of pressure thru the PRV, roughly 20% even before the piston moved. I double checked this by replacing the spring with a bolt so the piston can't move. With the spring, the valve would relieve more pressure as compressor pressure got above 60 psi, as I would expect a functioning PRV to do.
My question: Is this initial pressure loss, a) a function only of using air pressure, b) also present with normal operation with oil pressure, or c) because my PRV is bad?
For anyone interested, here is what I measured with the compressed air setup:
PRV testing | ||||||||||||||||||
comp psi | output psi | |||||||||||||||||
20 | 14 | |||||||||||||||||
30 | 23 | |||||||||||||||||
40 | 31 | |||||||||||||||||
50 | 40 | |||||||||||||||||
60 | 47 | |||||||||||||||||
70 | 54 | |||||||||||||||||
80 | 58 | |||||||||||||||||
90 | 61.5 | |||||||||||||||||