Welcome! Here are the website rules, as well as some tips for using this forum.

# how many gpm's is my pump?

Options
I guess you could start by telling us what it is?<BR><BR>Dave

• Member Posts: 5
Options
How many gpm's is my pump?

I need to install an air eliminator in a 7 storey apartment building hot water heating system. How do I figure out the gpm's of my circulating pump?
• Options
Flow Rate for Sizing Air Seperator

For a quick answer there are a few "assumes" involved (I don't like assumptions but here goes).

Assuming the flow is required to size the air seperator (meaning it does not to be very accurate - more like a flow range)

Assuming the air seperator is on the primary line (the main pipe for the boiler(s))

Assuming the temperature differential between supply/return at the coldest day is approximately 20 deg F, divide the boiler(s) total output by 10,000 to get a ball park flow rate. For example, if you have a total output of 1,000,000 BTU at 20 deg F the flow will be approximately 100 USGPM.

If any of those assumptions are substancially different than described or you truly want to know the flow across the pump you can use the pressure differential method (I can describe that proceedure if you like - it's fairly simple).

Congrats on the air removal device - it is a very important part of the system!
• Member Posts: 5
Options
The rest of the story

2-735k btu boilers each with armstrong S35 circ. pumps into main header and 1 armstrong H54(3/4H.P.) main circ. pump on return.
• Member Posts: 513
Options
Would you mind describing

the presure differential method anyway... I'd like to know.
• Member Posts: 2,440
Options
If I may

The DP method is to measure the differential pressure across the circulator and compare that, converted in feet of head, to the pump curve.
• Options
Pressure Differential Method

Here's the scoop...

Only works on centrifugal pumps - do not use on positive displacement or piston type pumps.

Get a performance curve of the pump you are testing. Remember, some pumps are multiple speed and some have trimmed impellers. The proper curve is a must (speed and trim is noted on the pump nameplate - or contact the manufacturer to be sure).

Read the shut off head in feet from the curve. Shut off head means head the pump produces at zero flow (far left side of the curve). It will read in feet of head, divide by 2.31 to get PSI (that is what guages read).

On the site, install pressure guages at the suction and discharge of the pump. Throttle the discharge valve to zero flow and subtract the suction pressure (PSI) from the discharge pressure (PSI). This is delta p (or differential pressure) and when multiplied by 2.31 should read close to the curve shut off head in feet.

Assuming it is OK, open the discharge valve to the position orgionally set and read the differential pressure in PSI, multiply by 2.31 and find the corresponding head point (in feet) on the curve. Follow down to the flow - that's it.

The key is the shut off head has to be confirmed OK for the pump you are testing. If it is off there is probably something wrong with the pump. If the shut off head is wrong so is the operating head.

This only works well with larger pumps (typically manufacturers have 1/4" guage tappings in these for testing). Residential pumps (pocket circulators) do not have these tappings as this proceedure doesn't work that well on smaller pumps.

Hope this helps. It is an excellent method for testing pumps without removing them from the system!
• Member Posts: 513
Options
So...

how do you do dat?

I put dis in before I saw da one below.
This discussion has been closed.