Strainer for fire pumps 2

[panteo]

Hope someone could recommend me a appropriate mesh size for suction strainer of fire water pumps.

We have installed fire water pumps recently as bellows.
1) Main pump #1: 3,000 GPM (Driven by electric motor)
2) Main pump #2: 3,000 GPM (Driven by diesel engine)
3) Jockey pump : 300 GPM (Driven by electric motor)
*. Discharge pressure: 10Bar
*. Water tank capa': 5,000 M3 ( H: 20 METER, D: 18 METER)

The problem is the suction strainers on the pumps.
It's 40mesh strainer. During the 3 hours test run, the strainer clogged. We consider that the mesh size is not chosen properly.
I contacted the manufacture of the pumps and received the data as follows.
*Maximum passing sphere size through impeller, single stage:
Maker: Peerless , fire pump. cetrifugal
Motor pump: 0.95 inch (Pump model 10AEF20)
Engine pump: 1.38 inch (Pump model 8AEF15A)

With above data, it's very difficult for us to decide the appropriate mesh size for the pump.
Someone told me that NFPA does not allow suction strainer for the fire water pumps. Is that correct?

Regarding the water quality, it's relativeley clean.
The water is supplied from the make-up water for cooling water.

Many thanks in advance.

 

[unclesyd]

Checkout either website they should have what you need.

http://www.lesliecontrols.com/Handbooks/Handbooks.html

http://www.mackiron.com/

 

[abcmex]

Panteo:
Ask you pump supplier for a recomendation.

If you compare the tolerable particles size against the holes of a 40 mesh I imagine that the conclusion is obvious.

Make a water analysis and check the material out of the clogged strainer. Does the analysis match with the material found? or someone forgot to flush the system.
rgs

 

[panteo]

Dear unclesyd, abecmex;
Thank you very much for your interest.
How about to remove the mesh screen in the suction of the pumps and install a new strainer in the inlet of the tank as following drawing?

http://www.antlove.com/fw.jpg

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Have a nice day.

 

[abcmex]

panteo,

The idea of filtering the water before the tank is a very good one, it avoid the typical problem of NPSH when you put a very small strainer before a pump.

I would still recommend to protect the (any)pumps against debris. The mesh size (holes) should be smaller than the Maximum passing sphere size through impeller. For sizing ask you pump supplier and check the pressure loss to determinate the required area.

Kind regards

 

[libertine]

i also like filtering before the tank, but have you considered using an open impellor which would possibly pump small particles?
Cheers!

 

[MJDLP]

According to NFPA 20 Standard for Stationairy Pumps for fire protection Chapter (6, Centrifugal pumps) 6.3.4.1 :&quot;Pumps that require removal of the driver to remove rocks or debris from the pump impeller shall have a pipeline strainer installed in the suction line a minimum of 10 pipe diameters from the suction flange.
6.3.4.2 The pipeline strainer shall be cast or heavy fabricated with corrosion-resistant metallic removable screens to permit cleaning of strainer element without removing driver from pump.

6.3.4.3 The strainer screens shall have a free area of at least four times the area of the suction connections, and the openings shall be sized to restrict the passage of a 7.9 mm (0.3125 in.) sphere. &quot;

Hope this answers your NFPA question.
Regards,

 

[Hookem]

The strainer mesh is quite often mistakenly chosen to maximum particle size allowed through impeller; instead, consider max. particle size allowed to prevent plugging small passageways to packing/seal areas.

The more you know, the less you know.