SteveSr
Well-Known OPE Member
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Hello,
There has been a lot of discussion lately about the effect of different Schrader valves on compression measurements. The physics says that the Schrader opening pressure is subtracted from your compression reading. In other words if your compression tester is reading 145 PSI and the Schrader valve requires 15 PSI to open then your real compression is 160 PSI.
I just bought a Mityvac 5530? compression tester and also a 10mm spark plug adapter with a Schrader valve from www.TinyTach.com and wanted to know the likely error caused by different Schrader valves so I set up a test with my air compressor as shown in the photos below
Test setup. The Mityvac pressure tester is there only for a low pressure gauge to read the result.
The test valves and the TinyTach adapter that I used for the test. The test subjects and results are as follows:
Clear - TinyTach valve - 10-12 PSI
White - Mityvac valve - 5-8 PSI
Red - bicycle tube valve - > 30 PSI!
Note: To get good measurements you really need a good secondary low pressure regulator. The standard on in my Makita compressor was rather fiddly at these lower pressures. Also while these valves will actually "pop" open the reading that you want is when the valve just starts to open and leak pressure.
I hope that this will encourage others to measure their Schrader valves and post their results. This way we can find the best valves and also know their effects on our compression reading results.
BTW, someone in another thread was wondering about adding a Schrader valve to adapters that didn't already have them.
Here I sectioned the bicycle valve so that you can see how one fits into the housing. Looks like one would have to have the proper tools and do some pretty good machining to get the valve centered and to seal properly around the colored gasket. Any leakage around the gasket would obviously invalidate the effort.
There has been a lot of discussion lately about the effect of different Schrader valves on compression measurements. The physics says that the Schrader opening pressure is subtracted from your compression reading. In other words if your compression tester is reading 145 PSI and the Schrader valve requires 15 PSI to open then your real compression is 160 PSI.
I just bought a Mityvac 5530? compression tester and also a 10mm spark plug adapter with a Schrader valve from www.TinyTach.com and wanted to know the likely error caused by different Schrader valves so I set up a test with my air compressor as shown in the photos below
Test setup. The Mityvac pressure tester is there only for a low pressure gauge to read the result.
The test valves and the TinyTach adapter that I used for the test. The test subjects and results are as follows:
Clear - TinyTach valve - 10-12 PSI
White - Mityvac valve - 5-8 PSI
Red - bicycle tube valve - > 30 PSI!
Note: To get good measurements you really need a good secondary low pressure regulator. The standard on in my Makita compressor was rather fiddly at these lower pressures. Also while these valves will actually "pop" open the reading that you want is when the valve just starts to open and leak pressure.
I hope that this will encourage others to measure their Schrader valves and post their results. This way we can find the best valves and also know their effects on our compression reading results.
BTW, someone in another thread was wondering about adding a Schrader valve to adapters that didn't already have them.
Here I sectioned the bicycle valve so that you can see how one fits into the housing. Looks like one would have to have the proper tools and do some pretty good machining to get the valve centered and to seal properly around the colored gasket. Any leakage around the gasket would obviously invalidate the effort.