Dead Men Tales: How Diaphragm Tanks Came To Be

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How Diaphragm Tanks Came To Be

In this episode, Dan Holohan shares some little-known stories about how diaphragm tanks were invented, as well as advice that will come in handy on the job.

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BradHotNCold

Homeowner here with a pressure gauge to check the pressure. But how do I "isolate the tank from the system" before testing for pressure?

Kevin2020

Thanks for the story Dan. And for all your others. They always make me smile and laugh. I've been a service tech for 30+ years and have met and seen a lot of the people and things you have. Brings back many memories. I'm happy I can still learn things too. Never thought about the semi-permeable membrane in an Extrol tank. Might be the cause of a dripping relief valve in my building. I'm going to check it out. Thanks again and keep 'em coming!
Kevin

MarkMurf

Had an old timer service dude who used to put a plug in the bottom of the air scoop beneath the tee to the system prv. Then he would put a tee in system supply after the scoop and mount the extrol tank up side down securing it to the floor joists with straping ! I was 16-17. Asked my dad(top shelf tech) about it."Ahhh, everybodys got their own ideas son, it's o.k . Walter does nice work. It works." Ran into him at a memorial service for yet another old oil burner service icon who had recently passed ."Hell'o Mr. Lucey, how are
ya ?" "Never saw Charlie's hands so clean kid." As we stood to the side of Charlie Matuzawitz laid out in the casket with his hands folded holding some rosary beads." Back in the day it seemed like we oil burner guys were a tight knit group. Friendly, mutually respectful.
"How come you install the expansion tanks like you do there Mr. Lucey ?"He always had an isolation valve with another tee tank side and a drain valve." "Servicability kid. And them new tanks seem to last longer that way. Thats all."
Everybodys got their own ideas. It worked.

Jamie Hall

At the risk of sounding like an antique (well, I am...) I remember when those things first started showing up in any quantity. I was in the water supply/well drilling racket at the time, and we started using them for controlling well pumps instead of the old hydropneumatic tanks (which, for any size at all, are a good bit more complicated than the compression tanks used for heating -- although it's the same principle). I don't mind saying that they made everyone's life a whole lot easier... And some of the ones I installed 50 years ago are still going strong!

DanHolohan

@BradHotNCold, you need a couple valves between the tank and the system. Read MarkMurf's post above. It allows you to isolate the tank from the system without getting soaked.

DanHolohan

@kevin2020, thanks for that. Means a lot.

mattmia2

You can also use something like this to get both valves in one fitting for isolation and drain:
https://www.supplyhouse.com/Webstone-40612-1-2-Threaded-Pro-Pal-Full-Port-Ball-Valve-w-Hose-Drain

DanHolohan

An even better idea. Thanks, @mattmia2

CLamb

My experience with tire pressure gauges is that they are very inaccurate--sometimes up to 30% off. Until I bought I high quality liquid filled gauge I never knew just how bad the others are.

DanHolohan

Good to know, @CLamb. Thanks!

mattmia2

Bourdon tube gauges are good as long as you don't drop them. The pencil type ones are worthless.

EdTheHeaterMan

BradHotNCold said:

Homeowner here with a pressure gauge to check the pressure. But how do I "isolate the tank from the system" before testing for pressure?

Lower the system pressure to a point below the static pressure needed. For instance, if you need 12 PSI for a 2 story home, lower the boiler pressure to 6 PSI. measure the tank pressure and if it is below 12 PSI, then add air until it is at 12 PSI. You see, 12 PSI will push all the water out of the tank into the 6 PSI of system pressure. Don't leave the system PSI down to long though. you will have a vacuum at the top of the system for as long as you are doing the test. That vacuum at the top air vents or loose valve packing will allow air to get sucked into the closed system. So keep that time to a minimum.

Once the pressure in the tank is where you want it, then fill the system with water back to the 12 PSI (or what ever you need) static pressure to maintain the needed pressure at the top radiators. Of course you may get a few bubbles of air up there, but that will all go away once you circulate the water in the system and those bubble pass an air vent, or bleed air from the radiators. That all depends on if you design your system to pump away from the expansion tank and have a strategically placed auto air vent. See Dan book on that subject for more details.



This is a diagram on how the system pressure will cause the pressure measurement in the tank to give you a false sense of security. The bottom row of tanks illustrates the tank pressure with no water in the tank. If you connect the tank to a system with 20 PSI water in it, the water will; compress the air in the tank to what ever the system pressure is, 20 PSI. The gauge will read 20 PSI no matter what air pressure you started with on the air side. I hope this illustration helps to understand the physics involved.

Mr. Ed

HVACNUT

Very interesting. If I was older I would have mentioned it in Dan's  "What did you think would never make it" thread. Whou'da thunk it?