pressure gauge

cutter

A while back I saw on here someone wanted a low pressure, pressure gauge. I was thinking and wondering if an air pressure gauge like what is used on the supply side of an acetylene regulator would work. That gauge is 0-15 psi in one pound increments.

A Taco 007-F5 says max pressure is 125 psi. I do not see how that is possible when they also say max head is 8.5 feet. Just a thought,

Can an air pressure gauge be used for water?

hot_rod

don't confuse the static fill pressure with the delta p the circulator adds when spinning.

The 125 psi is probably the maximum pressure the pump can handle, the delta P that the pumps adds to create movement depends in the piping circuit you install it into.

Here is a good read on pumps and circulation.
http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

cutter

hot rod said:

don't confuse the static fill pressure with the delta p the circulator adds when spinning.

The 125 psi is probably the maximum pressure the pump can handle, the delta P that the pumps adds to create movement depends in the piping circuit you install it into.

Hot rod, I guess I stuck my foot in my mouth. I forgot about the system pressure, you called it static fill pressure. And for that pressure gauge it would not know if it is reading the system pressure or any pressure above that created by the circulating pump. So instead a 0-15 PSI gauge a 0-30 Psi gauge would be a better choice. I also forgot I had saw them on the supply house site. SKU PFQ 802 and another SKU PFQ 902, don't know what the difference of the two are though.
That low pressure acetylene gauge was a dumb idea. You jogged my memory Thanks

hot_rod

Here are some suggestions from Winters for gauge selection.

Usually the boiler tridicator gauges, temperature, pressure, and altitude,
are 60 or 75 psi.

The actual reading on the gauge in a system will depend on where in the system it is located. At the discharge side of the circ, installed pumping away, the gauge pressure will be higher than static, fill pressure. When the circ pump is running, of course.

jumper

Altitude is important so you have to know how tall your system is above your gauge. Hopefully you have the minimum necessary when pump is off.

cutter

hot rod said:

Here are some suggestions from Winters for gauge selection.

I plan on using a gauge like you posted on the boiler plus just a pressure gauge on piping just after the boiler. I then thought about putting a pressure gauge on each zone after the zone valve, with the pump, pumping towards the zone. Those last gauges are most likely unnecessary.

The actual reading on the gauge in a system will depend on where in the system it is located. At the discharge side of the circ, installed pumping away, the gauge pressure will be higher than static, fill pressure. When the circ pump is running, of course.


Hot Rod, Another fellow on here suggested the .433 X the feet of elevation to top of system plus 5 psi. I used the Caleffi formula on page 47 of Idronics #10.
I am not a math person so I had my daughter work the formula. Using the cut/copy and paste I could not get the actual formula posted. And that #3 that is at the very bottom of the formula is supposed to be real small sort of above the ft.

My daughter used Microsoft excel and got a system pressure of 5.7 psi and that is after the additional 5 psi was added.

Formula B-1
Where:
Pa = air-side pressurization of the tank (psi)
H = distance from inlet of expansion tank to top of system (ft)
Dc = density of the fluid at its initial (cold) temperature
(lb/ft3)

I plan on hanging my expansion tank from the overhead with the inlet pointing down. so that would make H in my system be about one foot. Or does Caleffi mean where the pipe leaves the system piping going to the expansion tank? In my case that would be five feet.

I can't believe a couple of PSI would matter as long as air side and system side were the same on a bladder tank. And if the couple of PSI was on the high side not the low side.

Kind of got off topic here.

cutter

jumper said:

Altitude is important so you have to know how tall your system is above your gauge. Hopefully you have the minimum necessary when pump is off.

Right now I am running about 8 psi with a cold boiler. Is my gauge correct, who knows.
I am in the planning stage of modernizing my older boiler room design, if I succeed pretty much everything in the boiler room will be changed gauges and all.

hot_rod

The actual connection point into the piping established the PONPC.

Most fill valves and expansion tanks come factory set, or pre-charged at 12 psi, and that is typically the low side that systems are pressurized to. It is better to error on the high side of the pressure, as long as the expansion tank is sized and charged properly.

Pressure helps with air removal and can help quiet a chronically noisy system by squeezing the air bubbles and allowing them to travel back to the purger.

Some of the modern low mass boilers have pressure switches and may need a minimum amount of pressure to keep them from lockout conditions.

If the system runs fine with 8 psi, no problem with that. You might add a 30 psi gauge at the PONPC if you want to read low pressures more accurately.

jumper

cutter said:

jumper said:

Altitude is important so you have to know how tall your system is above your gauge. Hopefully you have the minimum necessary when pump is off.

Right now I am running about 8 psi with a cold boiler. Is my gauge correct, who knows?
I am in the planning stage of modernizing my older boiler room design, if I succeed pretty much everything in the boiler room will be changed gauges and all.

We're supposed to calibrate gauges in the shop and then check customer's gauge. Who does that?

rick in Alaska

I put in a brand new oil boiler and had to reset the pressure because it was reading low on the gauge. Old fill valve, so I thought it was just off a little. I re-pressurized to 12 psi and ran it a couple of cycles for the night. The next day the relief blew because the pressure was too high. Turns out the new gauge was bad. Also turns out, the fine print on the install manual says to not trust their stuff. $22,000 for the drying out crew and the lawyer. Thank God for insurance. So, check it yourself.
Also, why is it we have boilers where the block is rated at a maximum of 50 pounds, the relief valve is rated at 30, we pressurize to 12, but they give us a gauge that read to 75??
I want a 40 pound gauge for boilers. Right?
P.s. to Cutter: The "H" measurement you are looking at is not the expansion tank location, unless the radiation is all below it. The measurement is to the highest point in the system that the water has to go. If you are a single level house and the radiation is all below the expansion tank, then you would use that height.
Rick

cutter

Hot Rod, The measurement from the location where the pipe to the expansion tank leaves the boiler piping makes more sense than where the expansion tank is located. I will use that number for a new answer.
Even using 8 feet you get about 3.5 psi plus 5. The 8 feet is a little strong.

Several years ago I was running very low system pressure and was bleeding off air from coin vents. when I increased pressure to 8 psi or so there never was any air to bleed off. So I learned then to keep the system pressure where it belongs. Even with the low pressure the system was never noisy.

When I re-pipe this system I plan on putting in a pressure gauge here and there with a small ball valve between the gauge and system piping.

cutter

Jumper, I do have two boilers and I know for sure one of the gauges is wacko. I might buy a hose connection test gauge to check my gauge that I think is close. That gauge will be replaced even if it is good

cutter

P.s. to Cutter: The "H" measurement you are looking at is not the expansion tank location, unless the radiation is all below it. The measurement is to the highest point in the system that the water has to go. If you are a single level house and the radiation is all below the expansion tank, then you would use that height.
Rick

Rick, The H measurement I used is what I thought Caleffi was saying, that sort of did not make sense but that is what I thought the journal was saying.
I have a split entry house so 4 feet is below grade and a story and a half is above grade. The boiler sits on a pad 8 inches above the basement floor. I am planning on doing another calculation and see what I get. I was planning on using the location where the piping to the expansion tank leaves the system piping as the measuring point from there to the highest radiation. I am doing the calculation instead of using the .433 so I can size the expansion tank. That is the next step in Caleffi's math problem. To size the expansion tank is the only reason I am doing the math.