Pressure gauge public service announcement

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jblizzle

jblizzle

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May 19, 2010
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Tucson, AZ
I have one of the glycerin filled pressure gauges that I got from TFtestkits.net ... That thing is great!

Anyway I was just out of the pool and looked and it was showing a pressure of only 5 PSI which I thought was really strange. The flow seem to be good and my flow meter showed good flow so that left the pressure gauge. I popped the little vent plug off the top and glycerin came out and my pressure immediately jumped up to the expected 11 PSI.

Have to remember to let the gauge equalize as the outside temperatures are changing :)
 
If you do nothing will it eventually equalize on its own?

I've never fiddled with that plug on the back...


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No it seals pretty well so when temperature fluctuates, so will pressure. The error can be several PSI.
 
My plug is on the top, but I did not want to cut it so it would not leak. The design I have, I am not sure you actually could cut the tip off and have it auto- equalize.
 
The one I have has a small tip at the end of the plug and if you cut it off, there is very small hole the size of needle. But I bet you could just use a needle to poke a hole in plug and it should vent fine. With a small hole, the glycerin does not leak out very fast. You would have to have it upside down for a fairly long time for it to leak out.
 
Mine has a black rubber gasket on top with a small brass plug in it. I'd have to check the instructions that came with it (if I still have them) to see if I can just pull that brass plug. Never really noticed any pressure difference so I'm think I should leave well enough alone.


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With the brass plug, I think you can just pull it up and then back in.

I may check if there is a hole in mine, maybe add one. Still way better than the cheap non glycerin gauges!
 
Glycerin does not come out because the pump turns on.

As the temperature rises, the pressure in the gauge increases. This is what causes the gauge the read the incorrect PSI.

Initially some glycerin might come out because of the temperature rise. But not that much.
 
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So that's probably why mine has never shown an issue with this. The brass plug doesn't seem to be completely air tight so I think it allows the the increased pressure bleed out without letting the glycerine spill. This is the one i have -

Winters PFQ Series Stainless Steel 304 Dual Scale Liquid Filled Pressure Gauge with Brass Internals, 0-30 psi/kpa,2-1/2" Dial Display, +/-1.5% Accuracy, 1/4" NPT Bottom Mount

https://www.amazon.com/dp/B0087UY9AW/ref=cm_sw_r_cp_api_6na.yb7Y7DM1G


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So I did pull the black rubber plug off the top of the gauge again, and the pressure jumped 2psi. The act of pushing it back in made the psi drop again ... so clearly that is not good. Cleaned off the plug and indeed saw that I could cut just the tip to open up a small hole. Did that, put the plug back in and a little glycerin came out, but at least the pressure stayed the same.

Make me wonder what my real pressures have been the last few years :shock:

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Man Matt, those gauges are almost double the cost of the tftestkit ones ;)
 
Agreed, that one must have gone bad.

I have a large oil slick on my filter ... apparently air temps over 110 cause a good bit of expansion (plus the sun hits it too). Curious to see how "low" the level looks come the cooler temperatures
 
Just FYI for the future. There are several types of equalizer ports/plugs on these gauges. Very common is the snip tip plug, there's also the floating brass spool valve (like Matt's) that allow the gauge to equalize, but seal off if the gauge is turned upside down, then there's also one that has a little lever that you can open and close to allow the gauge to equalize (I have one of those). I'm sure there's a few more, but these are the most common.

Whichever style you have, you should make sure that the gauge can equalize due to changing temps.
 
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