Suction Strainer x Cavitation 1

[Mateus_R]

Hello,

I'm studying some topics in Fluid Power and I found on internet a recommendation to not install a suction strainer in the reservoir, on the suction line of the pump. This recommendation comes from the high pressure losses from the strainer, which could lead to cavitation problems in the pump? Or maybe from a maintenance point of view?

Thank you in advance.

 

[JJPellin]

I don't care for suction strainers. They are useful for a startup of a new unit or after replacing suction piping to catch weld slag and tape measurers. But, they should be removed after four hours in service. Permanently installed strainers will tend to drop suction pressure, making cavitation much more likely. If the solids are small enough to pass through the pump, you are usually better off to let them pass. The only other case where I supported the installation of permanent suction strainers was where we had chronic scrap metal making it to the pump (tray clips, nuts and bolts, tower hardware). Then I would install a strainer with the largest possible holes. The manufacturer of the pump should provide a value for the largest sphere that the pump can pass. Make the holes slightly smaller than that. In some of our pumps, we are forced to install suction strainers with smaller holes. In these, the strainer is not there to protect the pump, but is there to protect downstream equipment (usually heat exchangers) that could be plugged off.

You mentioned a reservoir. If this is about a lube oil system, then suction strainers should be installed. These should be positive displacement pumps with large NPSH margins. Cavitation is not a problem with lube oil pumps.

I should have started out asking what process you are looking at. What type of pumps?

Johnny Pellin

 

[TugboatEng]

Suction strainers can be used to prevent vortex formations when pumping viscous fluids. This is one reason you find them in lubricating oil sumps, that and engines often accumulate hardware in their sumps.

 

[Artisi]

Suction strainers correctly sized and positioned do not result in inlet problems, incorrectly sized or restricted by blockage are a problem.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Fluid power implies hydraulic fluid?

In general suction strainers are bad news as they are rarely big enough, accessible enough or cannot be monitored in use until you destroy your pump or the fluid flow stops.

Hydraulic fluid should be really clean and have few issues, but far better to put it on the discharge section if at all.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

Suction strainers should be greatly oversized to prevent plugging, or else not used at all. They only remove large particles that can instantly damage the pump. Fine filtration causes a relatively large pressure drop and will be placed after a pump.

 

[TiCl4]

Suction strainers should only be used if the expected solids to be filtered will cause issues with the pump. Examples of where I have seen them appropriately used include:

Slaked lime slurry centrifugal pumps.
Monomer emulsion rotary lobe pumps.
TiO2 slurry centrifugal pumps.

All are applications where detritus is expected to be large enough to not pass through the pump. I have personally seen cavitation and low flow in the lobe pump when the suction strainer filled completely with an shredded fragments of an unknown black rubber. Though cavitation and flow were problems, the pump could have been seriously damaged by those and other solids had they made it to the pump head.

Conversely, suction strainers were installed on the slaked lime application after unslaked lime pebbles both had pebbles catch in the impeller and had smaller pebbles erode the impeller away in a matter of days.

Appropriately sized, suction strainers pose no significant dP when clean, but will very likely cause pump longevity issues if they are operated fouled.

Put strainers on the discharge side unless you have a compelling reason to have them on the suction side.

 

[MJCronin]

Fundamentally, I agree with JJPellin ...

Suction strainers should not, as a rule be installed on pump suction piping .... Other measures should be investigated first, primarily sumps in the liquid reservoir, low suction velocities and possibly screens contained within tanks

In the extreme case where the nature of the process dictates that a suction strainer is absolutely necessary, the suction strainer should be a duplex "twin basket" strainer equipped with a "quick switchover" plug valve lever and a dp indication and switch. The switch should be alarmed at the control room and the local dp gauge checked periodically.

https://www.tateandale.com/wp-content/uploads/104-4B-Twin-Basket-Strainer.pdf

MJCronin
Sr. Process Engineer

 

[TugboatEng]

Screens in the tank are just very large suction strainers. I don't understand the difference? All of the problems described by everybody are resolved by proper sizing and fluid cleanliness. As someone who works in the field, I appreciate.tbe strainers as a last line of defense to keep out nuts and bolts that may end up in the reservoir. In that case, the perforations only need to be slightly smaller than the smallest nuts and bolts.

One particular brand of gearbox we operate spits the springs out of the detuner which takes out the oil pump and destroys the gearbox. The solution is to remove the detuner assembly and live with the noise but a strainer would also work. The noise isn't particularly loud, it just sounds like the gearbox is destroying itself.

 

[georgeverghese]

Use 2x100% inline basket strainers if you need larger dirt holding capacity on suction strainers. Y-type and T-type strainers are only good for relatively cleaner liquids. Where the pumped fluid is also the lubricant /coolant used in packed glands or simple mechanical seals, premature failure of these seals or blockage of seal flush lines can occur when the fluid has erosive particles in it.

 

[Mateus_R]

Thank you all for your answers. They were very helpful.
Btw, the system I mentioned was a lube oil system.

 

[goutam_freelance]

Generally speaking suction strainers are recommended by pump suppliers. The mesh size is fixed by the pump running clearances. So if you do not provide suction strainers you may not be able to avail manufacturer's warranty for new pumps.

 

[Tmoose]

Back in the mid 60s CHrysler determined the diameter of their Gen II Hemi's short (less than12" long) oil pump's suction lines was materially reducing the oil flow. Since the pump is some positive displacement type I'm thinking I have no clue what the proper description of the oil delivered to the system should be. Probably Not aerated. Maybe just a reduced volume and massive cavitation in the pump?

 

[1503-44]

Lube oil is not "fluid power".

 

[TugboatEng]

Suction stainers are on the suction side, not power side. There is no difference in application here.

For those of us working in the field without the cleanliness of OEM production, we like strainers. Give them to us but make them really big so we never have to clean them.

 

[1503-44]

Just trying to get some uniformity in terminology between fluid power and lube oil systems.

And in these applications, are they not usually called filters?

 

[TugboatEng]

If you want to get semantic, in the marine industry strainers are cleanable and filters are replaceable.

To be specific, a strainer protects the pump. The filter protects the system.

And, lubricating oil systems, due to the viscosity of the fluid, vortex generation can be a substantial problem. Many systems incorporate anti-vortex strainers which double as pump protection but are primarily for vortex breakdown. Lubricating oil systems and hydraulic systems that use oil with high viscosity generally require strainers..

It's important to know that lube oil systems are, ideally, low power fluid systems otherwise they would become parasitic.

 

[pawankashyap22]

[pre][pre][link growmechanical.com/2020/06/cavitation-in-centrifugal-pump.html]Link[/url][/pre][/pre][highlight black]Gas bubbles trapped in a centrifugal pump can adversely affect its operation. When the vapor bubbles collapse with high enough frequency, it sounds like marbles and rocks are moving through the pump. If the vapor bubbles collapse with high enough energy, they can severely damage the pump impeller.

It is importathe differenterstand different types of pump cavitation and its causes, before looking at how to prevent it.

Types of pump cavitation
Vaporization cavitation, also called inadequate NPSHa cavitation.
Internal re-circulation cavitation.
Vanepass syndrome cavitation.
Air aspiration cavitation.
Turbulence cavitation.
Prevention and Action measures to be taken against pump cavitation are discussed in the following sections.Gas bubbles trapped in a centrifugal pump can adversely affect its operation. When the vapor bubbles collapse with high enough frequency, it sounds like marbles and rocks are moving through the pump. If the vapor bubbles collapse with high enough energy, they can severely damage the pump impeller.

It is important to understand the different types of pump cavitation and its causes, before looking at how to prevent it.

Types of pump cavitation
Vaporization cavitation, also called inadequate NPSHa cavitation.
Internal re-circulation cavitation.
Vanepass syndrome cavitation.
Air aspiration cavitation.
Turbulence cavitation.

growmechanical.com/2020/06/cavitation-in-centrifugal-pump.html

 

[Artisi]

Pawankashyap, doesn't really address the OP's question, the OP was aware of the causes of cavitation but was really asking for thoughts on inlet strainers, plus he hasn't been seen for 2 months so it can be assumed his question has been answered.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)