5 replies to this topic

[CSNK]

Dear all,

I have double diaphragm pump. - motor driven.
In which there are two heads one is L-Head - represents Low head - Pressure is around 6-7 kg/cm2
Other is H- Head - represents High head - Pressure is around 17-18 Kg/cm2.

As per data sheet of this pump - it is mentioned that its rated flow is 40 LPH.
Now my doubt is that - can pump deliver more flow then rated?

I am new to the diaphragm pumps.
Thanks.

[ankur2061]

Chiks,

Have you thought of contacting the manufacturer / vendor of the diaphragm pump. Your question is simply related to obtaining the data from the manufacturer rather than anyone on the forum trying to speculate whether your pump can provide more flow than rated without any pump curve. And if you already have a pump curve you yourself can check out whether the pump can deliver more or not.

Regards,
Ankur.

[kkala]

A diaphragm pump is a positive displacement pump, so its flow rate is practically independent of the developed head, remaining almost constant at 40 lt / h. The two heads in the data sheet are understood to concern different discharge pipelines. For constant 40 lt/h flow rate, the head developed in one line was 6-7 kgf/cm2; while in the other line 17-18 kgf/cm2 (a line of the two may represent recirculation). See relevant performance curve of positive displacement pump at http://www.driedger....dp/CE2_PDP.html.
Membrane (and drive, if pump does not use compressed air) complies with the head of 18 kgf/cm2. Double diaphragm pump operation can be seen at http://www.versamati...d/aodd_demo.asp.
If "strokes per minute" (i.e. frequency of pulsations) is constant, flow rate is fixed, so it is judged that no increase in flow is possible for the pump as is.
Probably increase of "strokes per minute" (and subsequent increase in flow rate) is possible, if membrane (and drive, if any) can bear it. Only manufacturer can advise on the feasibility of this task.
In a fertilizer plant (1978) we had installed an air operated diaphragm pump with variable flow. If present pump had this possibility, its data sheet would have indicated flow range (not 40 lt/h).

Edited by kkala, 22 October 2011 - 02:51 PM.

[breizh]

I've attached a link related to air driven diaphragm pump manufactured by Wilden . At least you can get info about the technology and the performance of this type of equipment .

http://www.marcopump...II_Complete.pdf


Hope this helps

Breizh

[kkala]

Useful link, breizh, giving insight in air operated diaphragm pumps. On page 22 it is noted that "air inlet pressure has a direct relation to the fluid discharge pressure that the pump can develop (head), while the volume of air has a direct relation to how quickly the pump will reciprocate (flow)".
The pump in query is motor driven, but suppose it were air driven. Then air consumption (at standard conditions) and air pressure required are given by the diagram of page 71. Curves of equal air consumption indicate increase of liquid flow, in case of head decrease. For instance, the example of page 73 shows liquid flow 40 gpm against discharge of 40 psig, requiring 18 scfm of air at 60 psig. If liquid discharge pressure were constant at 20 psig (instead of 40 psig), 18 scfm of air would result in liquid flow of ~52 GPM, and required air pressure would be ~ 40 psig. Reduction of air pressure (60psig-->40 psig) is assumed to occur somehow automatically, adjusted to discharge pressure. So reduction of discharge pressure from 40 to 20 psig would increase flow from 40 to 52 GPM, to my understanding. Advice on this point would be welcomed. Air driven diaphragm pumps seem not similar to positive displacement pumps, and this should be considered as a correction to the previous post by kkala.
However a motor driven diaphragm pump is different, similar to other positive displacement pumps. Link http://85.185.231.19....AGM PUMPS.pdf indicates it (*). It is also noted there that "since motor driven, mechanically actuated diaphragm pumps are positive displacement pumps, capacities cannot be adjusted by the use of a throttling valve". Performance curve of motor operated diaphragm pumps must be as in http://85.185.231.19...AGM%20PUMPS.pdf, where "diaphragm operated PD pumps" are reported.

(*) Concerning the query, page 3.87 of the link is worthy of reading. It refers to Mechanical driven diaphragm pumps, Chemical and Water treatment industry.

Edited by kkala, 23 October 2011 - 07:08 AM.

[S.AHMAD]

1. For positive displacement pump, the volume per revolution is fixed. The pump capacity specified by manufacturer is based on certain speed.
2. The flowrate depends on the pump rpm.
3. This means you can increase the pump capacity by changing the pump speed
4. However, by increasing the flowrate, the pump discharge pressure (which is the line pressure drop + downstream pressure = back pressure) will also increase.
5. Thus, there is a limit due to pump discharge pressure (depending on piping configuration and downstream pressure - not from the pump)
6. High discharge pressure may damage the diaphragm