'Calculating' flow rate (GPM) to determine proper flow meter

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'Calculating' flow rate (GPM) to determine proper flow meter

Postby willemstockton » Mon 24 Mar, 2008 02:21

So I just started operating this acient pool. It was built during the FDR work programs with all donated material (on the pool house you can litterally see where they ran out of bricks, and used a different color/style)

I need to install a flow meter on the return to be par on code (not to mention basic calculation necessities.) Yet don't know what caliber i need. I don't want to pay an arm and a leg for a beefy one i don't need; and i don't want to install one just to have it max out.

It's not stamped on the motor nor turbine, the make and model number have long since rusted away so i can't call them up and find out, if they even still exist(It's seriously old, but runs like a champ. 30 HP, i swear the turbine used to be connected to a diesel motor...)

So, how can i figure it out, even a rough estimate will do.

I thought about setting like a 5 gallon bucket under my exposed waste line and timing it, but it's a different size pipe than the main lines, and i figured it would alter the results. Any suggestions?

You can email me at: willemstockton(at)gmail(dot)com

chem geek
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Postby chem geek » Mon 24 Mar, 2008 11:44

This must be a large commercial pool. Knowing the size of the pool in gallons will be useful as a cross check, assuming some reasonable turnover rate for the initial design. The 30 HP is equivalent to 22,371 Watts of power [EDIT] actually higher because one must multiply HP by the service factor (SF) [END-EDIT]. Though it’s hard to know the actual energy efficiency of the pump, it’s unlikely to be much above 50% so that would mean around 11,000 Watts of output power which will be equal to 0.188165 * Head (in feet) * GPM. To know the relationship between Head and GPM, one would need to know the system curve and that can roughly be determined by knowing the diameter and length of pipe, though it gets pretty complicated depending on elbows and types of outlets. However, if you have a pressure gauge on the filter, then we can estimate the suction head to be some proportion of total head (usually 15% or so). Then you can calculate GPM from the formula. For example, if the pressure-side head is 200 feet (200/2.31 = 86.6 PSI) then 11000/0.188165/200/(1-0.15) = 344 GPM.

I think you can figure a worst case by allowing for something like 6 hours for one turnover and knowing the gallon size of the pool. If the pool is 100,000 then the flow rate might be 100000/6/60 = 278 GPM or thereabouts.

Also, take a look at this PDF file for an actual commercial pool installation with a 215,000 gallon pool with a 15 HP pump that delivers 582 GPM at a Total Dynamic Head of 68 feet. One thing I forgot about in the above calculations is the service factor which for this pump is 1.15 (from the nameplate -- the text is wrong) so the actual power of the pump is 11185*1.15 = 12,863 Watts which is consistent with the 12.25 killowatt power consumption measurement (which is surprising since there should be some power losses from the motor itself -- brake HP which is HP times SF is supposed to measure delivered power from the motor without losses from impeller, not the energy input). The output power is 0.188165*582*68 = 7447 Watts so the efficiency is around 58%.

You should post at www(dot)troublefreepool(dot)com where a guy named Mark (mas985) can help you further since he knows fluid flow the best. There are also some other people with commercial pools who can help you.

(I've also E-mailed you this same info)

Good luck,
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Postby DBServices » Thu 27 Mar, 2008 04:57

Can you send a picture I can ID your pump. If its a 30 HP, flow rate will be between 1500 and 2400 GPM. I need the pipe sizes and the pump influent and effleunt presure and I can tell you the flow rate.
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Cleaning Peristaltic Pump Line/Tubing

Postby PoolBoy2010 » Sat 12 Jun, 2010 14:13

The facility that I work at uses a peristalitc pump (Rola-Chem 503), which seems to not want to siphon the chlorine from the barrel. The line feeds from the barrel upwards into the pump. Trouble shooting advises that the operator flush the tubing with a weak solution of (1/2 pint muriatic acid to one gallon of water). So, how is this performed? Do you take a bucket, mix the solution together, and allow it to feed into the pump and into the injector?
Pool Boy 2010

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