Pumps and Suction Strainers

To clarify - The strainer referred to is mostly used with a foot valve when pumping from a stream or a dam with a centrifugal pump situated above water level.

The total hole area must be big enough not to impede the flow even with some holes blocked.

If the effect of a partially blocked strainer is included in the NPSH calculations there should be no reason not to allow it.

As far as possible, NPSH should be calculated with strainer 50% blocked.

Pumping water out of a river or a sump, ok use the strainer.

Pumping in a closed circuit, like a circulating water pump in a power plant or a hot oil pump in a refinery, or a process pump in a chemical plant, then the screen should only be used for commissioning and then removed for running.

The main reason is that it is unnecessary as there should be nothing to protect the impeller from, and there is a risk (over time) of the strainer coming apart and going into the impeller.

Even in a closed circuit, workers tend to leave debris in the piping system during maintainance. Hence suction strainer is a good feature. Differential pressure transmitter/gauge should be provided to the strainer to learn the blockages.

That is why you put the strainer in for commissioning, and then take it out when the system is cleaned up...

The reason (the other person being me ) said that (it was explained too)

you put a suction strainer to protect the pump.

There is a contamination and the strainer slowly starts getting blocked

At a certain stage, there is a possibility that the block is so much that you get a heart attack ie cavitation.

For pumps it is necessary that the suction should be unhindered. So if you put a suction strainer, ensure there is a vacuum gauge too to protect the pump.

It was further mentioned that it is better to put a return oil filter/ strainer or a tank partition strainer ( we do either/both based on the requirement)

Was is not better to clarify on the same thread ? (Heat exchanger if I remember) so that repetition of information was not necessary.

Hello

Have a look to http://cr4.globalspec.com/thread/26513/Pump-strainer.

Hope this helps

I partially agree with you and partially not. Because in all the process plants the strainers are placed based on the property of the mediyum being pumped initially. The type of strainer choosen could be temporary or permanent. The temporay strainers are generally Conical strainers and permanent strainers are T-Strainers.

The temporary strainers are provided only during commisioning of the plant and the piping arrangement is made in such a way that the strainer can be removed out of function by means of providing a "REMOVABLE SPOOL PIECE". Once the pump is put down in normal operation after some cycles the strainer is removed allowing the medium to flow withour any distractions.

Hope this helps

Strainers should be used as mentioned earlier by other experts at the suction of the Pump. What type of strainers should be used is dictated by the time and application. At the time of commissioning fine strainers are to be used, which is obvious as debris is maximum during the first use. Later on coarse strainers, the size of which should be consulted with the pump manufacturer, should be installed.

So you are saying that a strainer of some kind should "always" be used?

If so, I am sorry to inform you that this is simply incorrect. I agree that there are applications where a strainer should be used. There are also applications where a strainer should not be used.

I also agree that consulting the pump manufacture is the best approach.

Dear Gautam,

As steve mentioned the strainer will not be in function always. As I mentioned earlier it is governed by the nature of medium and the frequency of cycles that will be put in operation. Thoufh it is kept in cycle for some time it the piping arrangemnt will make it inactive after the strainer performs its desired function of removing the coarse or fine debris whatever it may be so while commisioning.

Hope this helps.

Kumaran