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View Full Version : How to Calculate Feet of Head...???



Sherra
04-11-2006, 06:18 PM
How exactly would I calculate the feet of head for my pool? I've heard the term and seen it on the performance curve graph on my pump but have no idea how to figure out what it is for my pool. Is there a formula I should use to figure this out?

mas985
04-11-2006, 07:23 PM
It sounds as though the pool is not complete so you cannot measure it. With an existing pool you can measure existing head via the filter PSI and pump vacuum. However, you will need a vacuum gauge which you can get at Sears or OSH in the auto hardware section.

Some builders use 50' or 60' of head as a standard pool build but depending on the design, this can be way off. Also, most pool builders do not have the ability to do a head calc. You could hire a hydraulics engineer to perform one but it will be expensive. They also don't tell you that head is dependent on the flow rate through the pipes and the pump flow rate is dependent on the head. This is a circular calculation which requires an interative solution.

Also, the exact calculation is quite complicated and requires detailed knowledge of all the pipe size & lengths plus all of the fittings and equipment losses. If you are up for it there are some good references to get into the details but it does have a steep learning curve. I have detailed spreadsheets which do the calculations but again, the inputs need to be pretty accurate.

This approach may be best suited for your situation:

http://www.poolplaza.com/pool-pump-sizing-2.shtml
http://www.poolspa.com/publications/sin/stories/pumps.htm

Sherra
04-11-2006, 09:56 PM
My pool is complete. I've had water in the pool and the pump has been functional since March 13th. They poured the deck Thursday (I guess I should change my signature to take that part out). I could figure out what the measurements on the lengths of the pipes are within a couple of feet accuracy. I've got pictures of most of the plumbing before they backfilled also. I'm just trying to figure out how long I REALLY need to run my pump each day.

Sherra
04-11-2006, 10:13 PM
OK, I did a little more reading on those sites you linked, and it looks like my maximum flow rate is going to be about 42 GPM anyway because I've got 1.5" PVC pipe, so it looks like even assuming I could be running at my max flow rate I'm going to need to increase the length of time my pump is running...:cool: Thanks for the info!

mas985
04-12-2006, 01:58 PM
From your pictures, it looks like you have separate runs for suction and return which means you will have 1/3 of the total flow in each run. This is a good thing for 1.5" piping which is pretty small. So three runs of 1.5" pipe is close to the same loss as 1 run of 2.5" pipe.

Given that you are running your pump, what is the filter PSI? Multiply this by 2.31 to get return head. Suction head you can estimate from the web site and it should be fairly accurate. However, my guess is you probably have about 10' of suction head give the pool configuration.

Also, the 42 GPM is the maximum "suggested" flow rate for a single pipe and probably not what you may actually have. To get the flow rate, you must determine the head of your plumbing and look up the flow rate from your pump curves. This value could be well over 42 GPM. But since you have three pipes, you can go much higher.

Sherra
04-12-2006, 03:52 PM
I believe I've only got one return line leading from the filter which then "t's" off at the returns. :( That's the way it looks from the pictures I didn't put on my Yahoo site anyway. I'm guessing their logic on that is because you're less likely to get a clog in a return line??

My pressure reads about 15-17 right after backwashing.

mas985
04-12-2006, 04:58 PM
The loss between the filter and the tee is small compared to the loss over long lengths of pipe and through other fittings. Their design is fine and some perfer that over the single large pipe. Either way, the loss is nearly the same so I would not concern myself with that.

With that PSI setting, you have about 47 feet of head in your pool using 10 feet for the suction head. Now look at your pump curve in your manual to determine the flow rate.