No PTO pump pressure

[LouNY]

Here is an article from Fluid Power that is informative.

Fluid Power World

Pump suction strainers versus inline filter elements​

By Hilary Crisan | December 27, 2015
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David Marlowe • Owner/CEO • DMAR Technical Training and DMAR Business Centers USA


Approximately 80% of all hydraulic component failures are attributed to surface degradation caused by contamination and corrosion. Proper filter selection and sizing will provide years of reliable equipment operation and save money that is lost in fighting contamination-related failures. The cost of installing and

maintaining suitable filtration is estimated to be 3% of the cost associated with contamination related issues.


Let’s start with pump suction strainers. Contrary to what some people think, pumps do not suck liquids through the inlet or suction piping, but rather create a differential pressure (dp) at the suction nozzle. The fluid is then pushed into the suction nozzle in an attempt to equalize pressure.


Anything that restricts or reduces the fluid flow affects its efficiency. This results in less liquid being transferred, and thus reduces system efficiency (horsepower in compared to horsepower out). Any suction pipe that encourages the introduction of entrained gas or affects hydraulic flow instabilities in the liquid will result in a less efficient pumping operation. In addition to poor performance, truly bad suction piping will result in physical damage to the pump or its parts.


Pump suction system configurations are broken down into two parts:
1. Suction piping (proper diameter and spacing)—proper suction piping consists of pipe and pipe fittings, their relationship, quantity and relative location to the pump suction nozzle.
2. Suction source (NPSHA) design factors include:
• geometry of the source
• relative location of the suction entrance point(s) to suction liquid surface
• source enclosure boundaries
• other suction entrance points


Every pump’s successful operation and useful life expectancy is dependent on a properly designed and installed suction arrangement.


Some would contend that a true state of absolute suction is impossible (except in the perfect vacuum of



While many pump manufacturers caution against the use of suction strainers because of the damage they can cause, some designs, like Parker’s magnetic suction strainers, offer dual protection to the pump inlet without risk of cavitation.

space) and that only varying degrees of flow-causing differential pressure exist.


The term suction refers to the fluid acceleration toward the source (the pump). Pumps create a differential pressure, letting atmospheric pressure push liquid into a lower pressure area of the pump. Any impedance to unrestricted flow induced in this action will create instabilities in the fluid flow. The single most important function of a pump suction system is to supply an unrestricted, evenly distributed laminar flow to the pump. The pump suction system should not promote the introduction (or internal creation) of air, vapors or gas bubbles.


Improper designs of the suction piping, sump and/or inadequate pipe support exterior to the pump will create hydraulic instabilities in the fluid flow that result in destructive vibrations. In general, suction strainers do not contribute to system cleanliness.


Internal pump problems such as bearing failures, seal failures, excessive noise and vibration can often be accredited to sources outside the pump itself and the connected piping. The troubles created from poor suction conditions and poor piping practices will create unbalanced hydraulic flow.


To promote hydraulic stability and maintain a hydraulic balance on the pump’s rotating element, avoid direct connection of any type of pipe fitting to the pump suction nozzle. Pipe fittings cause pressure drops and turbulent flow patterns. Direct connection of elbows should always be avoided, as should 90° elbows. The only thing worse than a 90° elbow installed in the suction line would be having two of them!


It is important to select a filter that improves reliability of the hydraulic system to eliminate failures due to contamination. Let us look at the various options for the location of a filter. It is up to the system designer to locate a filter to support system operation, and location is subjective. The accompanying figure shows basic locations where filters are located in a lube or a hydraulic system.


The purpose of a suction filter screen is to protect the pump from large particles found in the reservoir. A filter screen is located on a suction port of the pump or attached to the suction pipe leading to the pump.


The filter screen is usually a coarse mesh filter. Inline filters are usually not placed on the suction side as high differential pressure can cause pump failure.


The micron rating of a fluid filter is a generalized way of indicating the ability of the filter to remove contaminants by the size of the particles, as seen below:
• 1 micron = 1 millionth of a meter
• 1 micron = 1 thousandth of a millimeter
• 1 micron = 39 millionth of an inch (0.000039)
• 25.4 micron = 1 thousandth of an inch (0.001)
• 40 microns = visible with magnification
• 40 to 90 microns = diameter of a human hair


A fine filter on a pump suction side would require a massive filter to handle the flow and have a low pressure drop. Fine filters load more quickly than coarse filters to allow the majority of small particles to pass. Improperly sized suction filters will cause pump failure due to cavitation. Many pump OEMs discourage the use of suction filters and suction strainers because of the inherent risk of pump hydraulic flow instabilities leading to cavitation.


Proper return filtration, transfer unit filtration and proper control of particulate ingression with high-efficiency breathers often make suction filtration unnecessary.


DMAR Technical Training
dmartechtraining.biz

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Filed Under: Fluid Power World Magazine Articles, Pumps & Motors
Tagged With: dmartechnicaltraining

 

[LD1]

looks like I put my reply into the quote above, sorry about that. I’m still learning this forum stuff. My reply starts with “ I repeat, I’m not arguing the terminology.
Whatever you say the name of a line is that’s what it is. So where do you think I should put the filter? You said it belonged in the return line coming from the valve. If I do that it’s no longer filtering what little comes out of the reservoir. Not gonna tap the reservoir, the T stays. I appreciate your help. But don’t tell me I know next to nothing about hydraulics when it was me who found the problem. (Air lock)

This is what is coming across as you having an attitude. Dont break your arm patting yourself on the back.

I specifically said I was NOT trying to insult you or be mean. Just honest.

I would NOT consider it an insult if you told me I know next to nothing about brain surgery or computer programming. Because its true....I dont. And if I were seeking help from experts....I would not constantly try and argue with them when they are trying to teach me some knowledge on their own free time.

Regarding your setup....if you refuse to tap the tank, then there is nothing you can do that is better than what you have besides maybe switching the filter to the return line.

Eventually all of the oil (even that in the tank) will go through the system and be filtered. If it didnt, you wouldnt have the tank.

IF You are worried about the oil on the reservoir not being filtered....if you have a suction bypass (likey with a 15 micron filter) you already arent filtering alot of that oil. And if you are worried....drain and flush the tank and top with fresh fluid.

Or keep it the way it is and it might last another 30 years.

But you are basically asking how to make it better....then in the next breath saying you are NOT gonna do the one thing required to make it better.

 

[Rich B1]

I have worked with hydraulics for the past 43 year. IMO, the ONLY thing that should be between a reservoir and a pump is a large hose with clean oil. Period.

Return line filtration is very efficient and is widely accepted within ag and construction industry. Why, it works.

Every system I have ever worked with that has something on the suction side ends up with a destroyed pump sooner rather than later. The idea of a filter/screen on the suction side sounds good in theory, but in practice, it shortens pump life.

If you filter on the return side, you are putting clean oil into the reservoir. In turn, the pump receives clean oil.

 

[CMR]

This is what is coming across as you having an attitude. Dont break your arm patting yourself on the back.

I specifically said I was NOT trying to insult you or be mean. Just honest.

I would NOT consider it an insult if you told me I know next to nothing about brain surgery or computer programming. Because its true....I dont. And if I were seeking help from experts....I would not constantly try and argue with them when they are trying to teach me some knowledge on their own free time.

Regarding your setup....if you refuse to tap the tank, then there is nothing you can do that is better than what you have besides maybe switching the filter to the return line.

Eventually all of the oil (even that in the tank) will go through the system and be filtered. If it didnt, you wouldnt have the tank.

IF You are worried about the oil on the reservoir not being filtered....if you have a suction bypass (likey with a 15 micron filter) you already arent filtering alot of that oil. And if you are worried....drain and flush the tank and top with fresh fluid.

Or keep it the way it is and it might last another 30 years.

But you are basically asking how to make it better....then in the next breath saying you are NOT gonna do the one thing required to make it better.

Thanks for answering my question.I read louNY’s attached report on suction filtering. So if the only way to improve my system is to tap the tank, I’ll consider it. It brings two questions to mind. Where should the return line enter the tank (top bottom or middle). and would putting a filter in the return between tank and valve reduce flow enough to cause concern? Seems like it might cause back pressure on the valve side of the return.
Also you said it’s likely I have a suction bypass because I’ve got a ten micron filter, but there is no bypass. Would it be an improvement to have one?

 

[CMR]

Thanks for answering my question.I read louNY’s attached report on suction filtering. So if the only way to improve my system is to tap the tank, I’ll consider it. It brings two questions to mind. Where should the return line enter the tank (top bottom or middle). and would putting a filter in the return between tank and valve reduce flow enough to cause concern? Seems like it might cause back pressure on the valve side of the return.
Also you said it’s likely I have a suction bypass because I’ve got a ten micron filter, but there is no bypass. Would it be an improvement to have one?

After reading RuchB1’s post forget that last question about the bypass. I’ll put a filter on the return or a screen on the tank but probably a filter on the return

 

[LD1]

Thanks for answering my question.I read louNY’s attached report on suction filtering. So if the only way to improve my system is to tap the tank, I’ll consider it. It brings two questions to mind. Where should the return line enter the tank (top bottom or middle). and would putting a filter in the return between tank and valve reduce flow enough to cause concern? Seems like it might cause back pressure on the valve side of the return.
Also you said it’s likely I have a suction bypass because I’ve got a ten micron filter, but there is no bypass. Would it be an improvement to have one?

Return line should be BELOW oil level so you dont aerate the oil.

No it wont reduce flow or cause noticeable backpressure. And most return filters have a ~25psi bypass so if the filter is overdue for changing and causing too much pressure differential it will allow oil to bypass and not blow apart. Some of the fancy filter housings even have a gauge on them to measure this pressure differential and indicate when to change the filter.

Regarding the suction bypass, for the most part you simply cannot tell by looking at the outside of the filter housing. You would have to remove it to know for sure.

 

[CMR]

Return line should be BELOW oil level so you dont aerate the oil.

No it wont reduce flow or cause noticeable backpressure. And most return filters have a ~25psi bypass so if the filter is overdue for changing and causing too much pressure differential it will allow oil to bypass and not blow apart. Some of the fancy filter housings even have a gauge on them to measure this pressure differential and indicate when to change the filter.

Regarding the suction bypass, for the most part you simply cannot tell by looking at the outside of the filter housing. You would have to remove it to know for sure.

Thanks. What about putting the filter on the return, without tapping into the tank, and leaving the T where it is? Rich B1 above says nothing should be between tank and pump period, but maybe he's just talking about obstruction, whereas the return line would just be adding more fluid to that suction line.
I can put a gauge at the intake of the filter and use a bypass.

 

[KWentling]

A lot of Peeing in the coffee cups today.
The OP's system wasn't unusual 40 years ago.
Today it would not be made for a few reasons. The filter being located between the tee and pump is a suction filter.
Suction filters or screens are usually used in a good system a return line filter is also used. The suction screens or filters filter out the coarse
contaminates that will rapidly damage the pump and valve often being a 50 mesh screen or 50 or 25 micron filter. At the same
time the return line filter can be a 10 micron filter to catch the smaller particles and maintain a cleaner oil.
One issue commonly found with the single line tank setup is moisture contamination of the fluid as much of the fluid lies stagnate in the tank,
the other issue that is quite common when one of these older systems gets worked hard is the temperature rise of the pressurized fluid as it is not circulated through the reservoir which also acts as a heat sink to cool the oil over temperature conditions can occur.
Also the top of the reservoir should be vented other wise pressure and vacuum conditions will be created in the system,
this will cause either vacuum leaks into or pressure leaks out of the system or both.

To be honest this is the first I've heard of a loader being plumbed this way. Maybe some of the old Farmhands we had in the early 70's that were old then were that way and I never had a reason to notice, or probably didn't have the knowledge to know it was different. Only took most of 3 pages to get an understanding of how it was plumbed. Maybe that's the only loader he has been around and thought they were all that way.

 

[CMR]

To be honest this is the first I've heard of a loader being plumbed this way. Maybe some of the old Farmhands we had in the early 70's that were old then were that way and I never had a reason to notice, or probably didn't have the knowledge to know it was different. Only took most of 3 pages to get an understanding of how it was plumbed. Maybe that's the only loader he has been around and thought they were all that way.

Maybe I'm done with your maybe's and just want my questions answered. I'm running a filter on the return and the return to the T and it will work just Fine.
THE END

 

[LouNY]

Be a good idea to add a filtered vent to your fill port;
Reservoir Accessories | Hydraulic Reservoirs & Oil Coolers | Hydraulics | www.surpluscenter.com
lots to choose from and inexpensive also.
Enjoy and have a good day.