10 replies to this topic

[Conchubhar]

Hello everyone,
I'm working on a project where it has been proposed to install a coarse strainer on the suction side of a pump, to prevent large objects damaging the pump.

The strainer is a flat plate, with as much 10mm holes as possible punched into it.
I'd like to calculate the pressure drop across it, and am wondering has anyone else come across something like this before. I estimated the DP by adding up the areas of each hole to get an equivalent area, and then used equation for pressure drop across an orifice.

Ideally I'd like to commission the pump without the strainer, then add it in later, and note the difference in pressure, but unfortunately it's on a cold LTC line, and the lines will be insulated and cladded before use.

[djack77494]

Conchubhar,
Your question is much too general to allow a meaningful response. Please define your fluid (LTC?) and key operating parameters such as pressure of the source vessel, vapor pressure of the fluid at operating conditions, etc. I can tell you that for Vacuum Tower bottoms, which I suspect is similar to your service, we typically allow for 200 feet of equivalent length of piping for the suction strainer. The dP is quite small, but the openings are large (as are yours), and the open area is ideally up near three times the pipe's cross sectional area. Please do not remove the strainer element before or during startup, since that will defeat its intended purpose.

[fallah]

Do you mean Low Temperature Condensate?

That strainer is considered as temporary or permanent?

Anyway commission the pump without the strainer isn't correct.

Why don't you consider cone type instead of flat plate?

[Qalander (Chem)]

Do you mean Low Temperature Condensate?

That strainer is considered as temporary or permanent?

Anyway commission the pump without the strainer isn't correct.

Why don't you consider cone type instead of flat plate?

Or A 'Y' Bucket type cleanable if more than one parallel pumps operating with due isolation block valve(s) provision!

[Conchubhar]

Djack, Thanks for your response.
I didnt define operating parameters/phys props etc as I dont consider it necessary. Take it as an incompressible fluid. 200ft equivalent length? sounds pretty big for a pump suction line, as with my case!

In my case - a simple plate with holes punched into it, the free area through the strainer is significantly less than the pipe cross-sectional area.

[SSWBoy]

Although I'm scratching my head for a way you could calculate the dP (with any sense of accuracy, i'll have a ponder at work tomorrow) just a quick note that you need to be mindful of the NPSH requirements of the pump.

[djack77494]

I didnt define operating parameters/phys props etc as I dont consider it necessary. Take it as an incompressible fluid. 200ft equivalent length? sounds pretty big for a pump suction line, as with my case!

Conchubhar,
May I reiterate - if you supply us with more complete information regarding your problem, we may be able to offer higher quality responses. Especially, the source vessel pressure and the fluid's vapor pressure are important.

200 feet of equivalent length is not very much. In fact I'd be more comfortable if the value were increased. If you calculate the dP for that length, it is likely much smaller than typical "throw down" values used for strainer dP's. But then, pump suction lines require a bit more care than most pressure piping.

I really don't like the simple plate with holes. The dP will be much higher than for a commercially purchased strainer. You're asking for trouble if you go that route.

[Brenno]

Im not looking for someone to do an NPSH calc... consider this a theoretical question - how would one calculate the pressure drop for an incompressible fluid across a plate of D diameter with N no. holes and each one of these of d diameter.
I agree that a commerical strainer is preferable - the homemade plate is an equipment item that has been used on site before (and it's popularity seems to have increased to every new pump), no major disaster has happened, but no knowledge of potential pressure drop, or even how to calculate it, leaves me feeling uncomfortable when my client demands it!

[SSWBoy]

What is the flow-rate and diameter of pipe?

Also,

http://www.eng-tips.....cfm?qid=205170

[proinwv]

Let me throw my comments in here.

First, the total area of the holes and a Cd (where will you get this from) will not work. There is much more involved with this type of strainer.

Second, your calculations are only useful for the first few minutes of operation. Your strainer, works, it collects trash, the flow reduces.

[Qalander (Chem)]

Let me throw my comments in here.

First, the total area of the holes and a Cd (where will you get this from) will not work. There is much more involved with this type of strainer.

Second, your calculations are only useful for the first few minutes of operation. Your strainer, works, it collects trash, the flow reduces.

Hello/Good Morning& Thanks Paul;This is exactly the concept missed somehow by the OP.

Dear Conchubhar Hello/Good Morning,

You should think/envisage about

the surface area availability/ Non-availability for filtering out on progressive basis

This area will markedly reduce

in case of fouling/retaining of the solids or any debris meant for removal.

Rate of reduction in effective surface area availability depends on solids,debris or other unwanted materials %age contents need removal.