The Stovebolt Site Forums The Shop Area The Tool Chest Schrader valve - compression tester

Is there anything unique about the Schrader valve in a compression tester, or is it just the same as any other Schrader valve?

Need to replace mine.

I don't know much about them but they all should be about the same design.
The difference may be in the pressure ratings and what industry/applications they are used in.
I do know that Nuclear, Safety related grade for nitrogen are really high dollar.

Don

Yes they are different, different pressure rating. I keep a couple of spares in my tester case just in case one goes south when using it. I'm guessing you can get them from H/F

Nathan - From what I've read, the "Schrader valve" in an engine compression tester is noted to be a "low tension" unit. Different than non-tester valves. They seem to be carried by various vendors on-line.

An example would be Box of 5 Milton Deluxe Compression Tester replacement valve cores OR Lisle Compression Tester Replacement Parts 20100 (order by each)*

* Look up your tester Brand/Model to see if you can find a specific replacement product.

One of my compression testers doesn't use a Schrader valve, just a pushbutton valve to release the pressure. Maybe that's because it's rated up to 1000 psi for diesel engines.
But the one for gas engines seems to have a standard Schrader valve core. It's only rated up to 300 psi. Again, it's just serves a release function. The check valve is between the Schrader valve and the connection for the spark plug. So I don't think it would need to be a low tension design. But if there's a Schrader-looking valve in the spark plug adapter, then maybe so. The one behind the spark plug adapter on my gasser tester doesn't appear to take any less pressure to open it when pushing on the stem.

If you have a valve core removal tool, just unscrew it and compare.

A compression tester is a good example of the "measure with a micrometer- - - -mark with chalk- - - - -cut with an axe" principle. Its only practical use is to get a percentage variation of pressure readings from one cylinder to another. The actual pressure indicated on the gauge is irrelevant. If you want an accurate indication of how much pressure a cylinder can hold, do a cylinder leakdown test with compressed air. Why would anyone be concerned if it takes 3 PSI instead of 1 PSI to unseat the Schrader valve? Try using three different compression gauges to check the same cylinder. I'll be surprised if they read within 10 pounds of each other.
Jerry

Backstory here…..

Loaned my gauge to a friend. It wasn’t working so I had him check to see if the valve was messed up, and it was. Spring was all jacked up.

He put a valve in it from a bicycle and tried again. Wouldn’t read over 80 PSI. So he bought his own and had compression on that gauge in the 125 range.

I figure I will buy the compression gauge-specific Schrader and see what happens.

This is your opportunity to buy a leak down tester as suggested by HRL. Better still, if you have a birthday coming up, your wife can buy if for you. Or Father's day?

She is pretty lucky to have me. I will start dropping hints.

For the price of a fancy cup of "coffee" and a couple of donuts, why don't all of us have a leakdown tester? I've been using one I built from bits and pieces of a paint gun pressure regulator for 20-something years!

www.ebay.com/itm/387387112285?

Jerry

In my feeble mind, a compression gage is all I need to compare the cylinder pressure readings
If they are not close to the same, it's time to start planning a rebuild.
Start with the heads, then cylinder wear and if you go that far, you might as well keep going on rings, crank bearings and cam.
Timing gears/chain also.
I have not rebuilt many engines, but every time I started with a valve job I end doing a full rebuild.

Don

That should be one of the basic food group tools. Some people don't have one??