Low capacity Diaphragm pump - sizing suction and discharge
Low capacity Diaphragm pump - sizing suction and discharge
(OP)
Hi.
I am trying to size a pump for a client, to output chemicals from an injection pot to an overhead tank. The capacity of the pump they want is in the 10gallon per hour range (the chemical injection shot pot is 2 gallons in volume). However, I am getting very small values for suction size based on a velocity of 1f/s at the suction side (less than 0.5 inches), as mentioned in API 14E "typical flow velocities".
Does anyone have experience on sizing the suction / discharge lines for such low capacity pumps? Or to be more precise, anyone sized chemical injection pumps with suction size of 0.5 inches?
I am trying to size a pump for a client, to output chemicals from an injection pot to an overhead tank. The capacity of the pump they want is in the 10gallon per hour range (the chemical injection shot pot is 2 gallons in volume). However, I am getting very small values for suction size based on a velocity of 1f/s at the suction side (less than 0.5 inches), as mentioned in API 14E "typical flow velocities".
Does anyone have experience on sizing the suction / discharge lines for such low capacity pumps? Or to be more precise, anyone sized chemical injection pumps with suction size of 0.5 inches?





RE: Low capacity Diaphragm pump - sizing suction and discharge
RE: Low capacity Diaphragm pump - sizing suction and discharge
However, lets remember that this kind of pumps doesn't give you an uniform flow, but pulses of high-low flow. This can be avoided with a surge tank, but this will be an extra equipment you'll need to consider.
You may want to consider a metering pump or a peristaltic, (LMI Milton Roy is a manufacturer, I don't remember another right now).
RE: Low capacity Diaphragm pump - sizing suction and discharge
Are you considering a centrifugal pump? why not look at eccentric screw pumps for such low flow application?
Can you provide details about head ?
Wimple
RE: Low capacity Diaphragm pump - sizing suction and discharge
Rickfer, for one application the flow is to a heat medium system make up tank, so intermittent flow isnt a problem. The second application is to another pump suction. However, a pulsation dampener should help reduce effects of high low flow, as you call it. The pictures i have seen of pumps suitable for this kind of application are very small pumps, they can actually fit in my hand! I'm not very experienced with pumps for such low flow.
Wimple, we are considering a pneumatic diaphragm pump. Total head needed is no more than 9 feet.
RE: Low capacity Diaphragm pump - sizing suction and discharge
Smallest pump I know has 1/4" NPT connections and fits on a 6"x6"x6" box, and can flow up to 3.1 gpm.
Remember that this pumps operate different that centrifugal pump. You can adjust pump flow by adjusting inlet air pressure and flow (with the FRL).
If you need to change the flow head, you need to change the inlet air pressure. If you need to change the flow, you need to change the inlet air flow.
If you need to control the flow, you may need the surge tank and a control valve.
Regards,
RE: Low capacity Diaphragm pump - sizing suction and discharge
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Low capacity Diaphragm pump - sizing suction and discharge
Vary the pulse rate to vary the flow.
Roy
RE: Low capacity Diaphragm pump - sizing suction and discharge
BigInch, I am assuming you mean to increase the suction pipe diameter in lieu of a larger surge tank, right?
With a flow of 10gph [just under 0.2gpm], the flow velocity for a half inch pipe comes to about 0.28ft/s. This is far lower than recommended velocities, but as i was at pains to explain to my colleague yesterday, these recommendations (API 14E, for example) mention the words "if practicable".
In the first case, for the heat medium system, the client expressly asked for a "small, pneumatic pump with a flow of 4 - 6gph". The original design was supposed to be by gravity flow to the make up tank, but the installers installed it at a lower elevation than the make up tank, hence my designing a pump. The pot is only 150mm diameter and 450mm height [2 gallons when full] and is filled manually, hence the low flow needed. I figure a design margin of 10gph pump should be adequate.
The second case, for the cooling water system, is similar (same size pot, same flawed installation with not enough static head) but they want to bypass the makeup tank and instead pump chemicals directly to the suction of the cooling water circulating pumps. The discharge pressure head is the pressure at the suction of these pumps.
(I realise i should have described the system in more detail earlier)
Anyways, my question now is, has anyone worked with such low velocities with such pumps? 0.3 ft/s seems quite slow.
Regards
RE: Low capacity Diaphragm pump - sizing suction and discharge
If the fluid has/gives no problems flowing slow, let it. Its going to be equally as hard making the suction line smaller than 1/2 inch. The alternative is to dose the line for a few minutes at higher flow and shut it down until its time for the next dose.
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Low capacity Diaphragm pump - sizing suction and discharge
OD tubing and compression fittings are commonly used for linesizes lower than 1/2" NPS such as for metering applications. With proper routing and support, they perform extremely well, for far less than the installed cost of pipe.
RE: Low capacity Diaphragm pump - sizing suction and discharge
The Client specifications rule out anything less than 1/2" NPS pipes for this service of fluid. But thanks for the input.
BigInch,
the client was happy the size / flow. So i think this issue is solved now. Thanks to all who made an input.
I think the thread can be closed now. Err...who closes it, exactly?
RE: Low capacity Diaphragm pump - sizing suction and discharge
Johnny Pellin
RE: Low capacity Diaphragm pump - sizing suction and discharge
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Low capacity Diaphragm pump - sizing suction and discharge
Just a point for your consideration. I work in the water treatment area, and depending on the chemical you're pumping, you might want to consider small magnetic drive gear pumps. They're available in exotic metals (e.g. titanium, stainless steel, Alloy 20, etc), as well as various high tech polymers, and because the magnetic drives, you don't have a seal to deal with, and the output flow is very nearly pulseless. Flow can then be monitored with a small mag-meter, and you're all set. For flow control, you can either go variable speed, but if your required flow turndown is too great, simply put a relief valve back to suction in the flow loop (it's a positive displacement pump after all), and connect the discharge line to a flow control valve. Use the valve to meter the flow. Yes, there's a bit more power loss, but control wise it's smooth and simple control that you can set "right on the money". For most water treatment chemicals, we've found that any stuff in the as-furnished chemicals contains soft sludges, so filtering is commonly not necessary. At my plant, we've been doing this for a decade or so. Works real slick.
Then you don't have to worry about vibrating piping and hard-to-measure flowrates.
Just a thought.
RE: Low capacity Diaphragm pump - sizing suction and discharge
I agree with your recommendations. There's nothing better than a nice smooth stable flow with moderate velicities.