Will the Real Compression Test Please Stand Up!

[asauer]

So does anyone have any recommendations for quality gauges?

 

[lone wolf]

Once the valve opens the gauge is going to see the full pressure.

Right again.

 

[lone wolf]

So does anyone have any recommendations for quality gauges?

Snap on works good but are pricey. I have one that lasted 25 or more years.

 

[lone wolf]

Here is a gauge I made its US Gauge and a Snap On adapter hose.

 

[blsnelling]

WAY over thinking this!

 

[lone wolf]

WAY over thinking this!

They always do . I would take your word for it.

 

[blsnelling]

It takes x PSI to open it, but once it's open, what's there is there.

 

[lone wolf]

It takes x PSI to open it, but once it's open, what's there is there.

That makes sense to me.

 

[Deleted member 117362]

It takes x PSI to open it, but once it's open, what's there is there.

Agree. If they have less than 10psi, going to need a lot of work.

 

[lone wolf]

Agree. If they have less than 10psi, going to need a lot of work.

I never seen one with a piston still in push less than 60 psi.

 

[rwoods]

It takes x PSI to open it, but once it's open, what's there is there.

Not so, the spring is still exerting it’s pressure to close the valve. But I agree that with the right valve who cares - you use the gauge reading.

This is close to becoming an oil thread. So I am agreeing to disagree and I am out. Not mad or anything - just have more productive things to do.

Ron

 

[lone wolf]

So does anyone have any recommendations for quality gauges?

Snap on is good for sure in my own humble opinion. If not in your price range look at OTC.

 

[Deleted member 117362]

Not so, the spring is still exerting it’s pressure to close the valve. But I agree that with the right valve who cares - you use the gauge reading.

This is close to becoming an oil thread. So I am agreeing to disagree and I am out. Not mad or anything - just have more productive things to do.

Ron

But once you are above that pressure it's open. At spring pressure and above, is it not open? No problem here, enlighten me.

 

[kevin j]

It takes x PSI to open it, but once it's open, what's there is there.

Nope, that’s the point: It doesn’t open and stay open, it needs x psi differential across it and once flow stops into the gauge, the valve closes, holding that differential pressure. The gauge never reaches tghe cylinder pressure.

Here’s an experiment: put a tire valve into the compr tester and do a test again, It will be way low on the gauge.

If the valve truly stayed open, there would be no need for the special schrader valve.

In practice, it doesn’t matter as the valve spring is so small with the proper valve. But this is the reason you can’t use tire stem valves, and have to buy the $2 ones specifically for compression gauges.

For compr gauge, just use the right valve. But understand the concept if you set relief or pressure regulating valves.

 

[TheTone]

It takes x PSI to open it, but once it's open, what's there is there.

Not so, the spring is still exerting it’s pressure to close the valve. But I agree that with the right valve who cares - you use the gauge reading. This is close to becoming an oil thread. So I am agreeing to disagree and I am out. Not mad or anything - just have more productive things to do.
Ron

I think Brad may be referring to the tire valve which is pushed open by the mechanical force of the hand holding the tire gauge. Once open and HELD open, it's as if the tire valve was not even there. This situation is quite different from that where the compression gauge valve is being opened (but not held open) by the compression pressure within the cylinder. Does that make it clearer?

 

[lone wolf]

I think Brad may be referring to the tire valve which is pushed open by the mechanical force of the hand holding the tire gauge. Once open and HELD open, it's as if the tire valve was not even there. This situation is quite different from that where the compression gauge valve is being opened (but not held open) by the compression pressure within the cylinder. Does that make it clearer?

What would make it clear would be does a compression gauge give the exact correct numbers that are in the cyl?

 

[dswensen]

Sorry I asked gents .....

 

[HarleyT]

Hey,
it's winter......

Let it pile high!!!

 

[TheTone]

What would make it clear would be does a compression gauge give the exact correct numbers that are in the cyl?

Let the pile continue:
Compression gauge reading = Actual cylinder pressure minus opening pressure of gauge Schrader valve.

This is the reason for the special Schrader valve . . . to make the opening pressure approach zero.

 

[HarleyT]

Let the pile continue:
Compression gauge reading = Actual cylinder pressure minus opening pressure of gauge Schrader valve.

This is the reason for the special Schrader valve . . . to make the opening pressure approach zero.

My mother always said that I was "special"....