Contamination Control

[stroupaloop]

Being that contamination control is one of the largest concerns in today's fluid power industry and I noticed no recent posts regarding the topic, I thought I would bring it to the table with a starting question.

Can anyone accurately convert micron sizes from ISO 4402 to ISO 11171 for any given micron value?

...go...

 

[budt]

I entered ISO 4402+ISO 11171 in Google Search and came up with some 993 hits.

Here is one from another Forum.

http://maintenanceforums.com/eve/forums/a/tpc/f/319103451/m/8591099231

Also:

http://natrib.net/publications/articles/4Q01whitefieldside.php

BTW, I have yet to come across hardly anyone in industry in my area who would have any idea what the standards are and even if there are any. One company with 2,500+ employees has a department who checks fluids but seem to have no input when it comes to specifying what kind of filtration is required.

I find Filtration is another whole area of Fluid Power that is overlooked at best and downright left out on any hydraulic circuit except those using Proportional or Servo Valves. Filter the fluid or don't run the machine if it has these valves.

Many machines I have worked on have at best a 125 Micron Suction Strainer plus nothing else.

I relate that lack of applying Filters to the lack of knowledge in the Fluid Power world.

Had two machines with two 185 GPM Radial Piston Pumps each that were being rebuilt as many as five times a year and everyone thought that was normal.

Installed some LAARGE 5 Micron offLine Filters on the 5,000 Gallon Tanks which only lasted about two hours before going into bypass so we changed to 10 Micron until they started lasting a week or more. Then went to the 5 Micron Elements and they finally are up to about two months before starting to bypass. These were not small filter units either.

Now the pumps, which run 24/7/5 run 5-7 years and are changed out now due to reduced cycle time not a full Crater condition.

BTW, A pump rebild cost's about $18-22,000 each since the company that made them went out of business some 25 years back.

I specify a Suction Strainer on all pumps and on Piston Pumps of larger size I use a fixed volume pump to Super Charge it so it will not be subject to cavitation. I use a Pressure Switch on the Super Charge Pump out let that will not allow the main pumps to start and will shut the pumps down when pressure drops below a minimum level. The PLC is warned of increasing back pressure so filters can be changed at regular hut down periods.

The Super Charge Pump pushes the oil through a 5 Micron filter before it goes to the pump/s and all excess flow is the OffLine filterin loop.

On the Return Lines I use a 10 Micron Non-Bypass Filter with pressure indicators to monitor Back Pressure to give a visual and/or electric feedback signal that warns of the need for filter change or shuts the pump/s down finally at the next cycle end.

Some call it OverKill but no one complais when pumps run 10 years 24/7/7.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[stroupaloop]

Bud,

You are absolutely correct. For the most part, many "hydraulic" engineers only know the very fundamentals of how to design a system, yet alone being able to design for reliability. Numerous times have I gone to a company during a consultation visit and was astonished at their reliability issues. Fortunately I've noticed the large increase in the military's decision to increase system reliability, requiring companies to comply with MTBF (Mean Time Between Failure), which forces them to understand reliability principles for hydraulic issues, including contamination control.

On the topic of 4402 and 11171, few even know about the differences involved here. 4402 was the original Particle Counter Calibration definement, whereby they designated the micron sizes of particles. When 11171 came out, specifically pushed by Pall Corporation, the micron sizes changed. This didn't alter the amount of dirt or the sizes of particles within the same fluid measured with 4402, just redefined the particle size.

The question is whether loaded and requires quite an interest and work because comparing the two equivalent micron sizes generates a non-linear comparison, which does not allow an easy conversion. I've seen some conversions, but inherently knowing fixed points of conversion, the equation does not hold true for all sizes. Thus the question.

As far as filtration goes in systems. It is great and wise to incorporate a coarse inlet filter to catch all potential large particles entering a pump and a well defined clean up filter in the return line. I'm sure you've had experience with this, but if you are having difficulties with pressure or longevity of filter life, you may try double staged filtration with a bypass relief valve. Although everyone desires, or should desire, high filtration processes, the smaller the micron rating on a filter, the faster the holding capacity becomes, increasing change out time. One approach to solve such problems is to create a two-stage process, where the fluid first becomes filtered through a higher micron filter, such as a 15-25 micron, and then enters a finer filter like a 5 micron. This allows for a longevity of life, decrease in replacement time and typically a reduction in cost to meet the same performance parameters.

Sidenote, when using a Super Charge pump to reduce cavitation for your main pump have you ever investigated using a booster pump such as a centrifugal pump. Typically I've noticed that those work quite well and provide the sufficient amount of inlet pressure required for such application.

Additionally, even people that are in the contamination control industry commonly forget things such as cavitation in the pumps creates contamination, but this contamination is air. Contamination ranges from air, water, heat, mechanical and biological which all have different characteristics of abrasiveness to a hydraulic system.

 

[hydromech]

I lost a job over contamination control!

The company I was working supplied marine equipment from the UK to the US Navy and CG.

I set a workable target for oil cleanliness of 18/15/12 to ISO 4406. The ethos of the comany was, and still is build them cheap and sell them high and I am talking millions of dollars.

The CG were bang on with the idea of keeping systems clean to maximise reliability. The US Navy, for the most part had not got a clue what keeping oil clean meant to reliability.

Anyway...I was the hydraulic systems engineer and had total responsibility for the design, commissioning and service of all fluid systems. After a trip away I came back to system being built that had oil that was measured at 23/22/19, very dirty. I set about getting it cleaned up, but the senior management just wanted it out of the door to get the cash in. I would not sign to say that it was ready for on board commissioning so I was told to leave.

After that I quit hydraulics as it seemed that it was to difficult to get anyone to realise the importance of keeping oil clean.

It was tricky enough when ISO 4406 was changed over to the medimum test dust. The introduction of 11171 standard is just another example of the hydraulics industry shooting itself in the foot.

Adrian

 

[stroupaloop]

You are right, its so difficult to get a good moving concept of what should be done in hydraulics, but I suppose thats the ever lasting battle we deal with.

To be honest, I'm not surprised to see it happen because for the most part people that do have the "knowledge" of hydraulics understands the lack of knowledge in the world and the capital gain for them that can come from it.

For instance, regarding the 11171 change. You know who made it...well I told you, but its Pall Corporation, one of the leading filter companies in the world. The main goal is sells and business. They had a very intelligent man with the last name Bench, who originated from the contamination control era at the FPRC and he saw the opportunity to change the standard. Did that change the physical size of particles...of course not, but did it make Pall's filters look better when he was VP, of course and did they get more sells, always. I suppose its just interesting to see such things happen and it will never truly be solved until fluid power is mass taught to the industry beyond a 3 hour technical course that the company sends their employees to to learn Pascal's Law.

On a sidenote, I'm stunned, but not surprised about the lack of contamination cleanliness requirement by the Navy, but hopefully it has gotten better.

How long ago did you have this position?

 

[hydromech]

I left that job in January 2006.

Before that job I worked for a Parker Hannifin distributor. Even then I was amazed at how everyone would try to screw everyone else over. Not just just competitors but also other Parker distributors. So desperate to get orders, they would cut the job to the bone using just enough hardware to meet the spec.

Filtration was used as a device to get a pump through warranty. Nobody would care if a pump failed after 12 months use.

Now I design fuel,oil and water pumps for commercial diesel engines. It's just not the same, but it pays the bills!

Nobody appreciates a good hydraulic systems engineer!

Adrian

 

[stroupaloop]

Very true. My wife is looking at law schools right now and most likely Boston or DC, more DC then Boston, and I've been looking around to see what hydraulic engineering jobs are available at places like Monster and its hard press to find a job with the title "Hydraulics Engineer."

 

[budt]

stroupaloup and hydromech:

Welcome to the real world of Fluid Power.

I would like to say it has changed since I started in 1959 but unfortuantely that is sadly not the case. AND, if feedback from this and other Forums is any indication I will probably not have mind enough to see the change if it ever comes.

When I first started talking about the need for trained/dedicated Fluid Power persons in 1988, I compared it with our sister states Prohibition Laws. No Alchoholic Beverages can be sold legally except in clubs you have to pay a membership to or in most of the Counties that are on the border with states where alchohol sales are legal.

Every few years the law comes up for a vote to repeal it and is struck down by a good margin. I always thought it was the religious right that was the driving force to keep the law on the books. However, to my surprise, I found t was actually the BootLeggers who were the main Lobbying effort against repeal. They have a vested interest in keeping the law in effect since they can sell all the alchohol they can get and not pay taxes to boot.

So maybe it's the Fluid Power Manufacturers and Distributors who want the StatusQuo???? A lot of money is made designing circuits, Trouble Shooting and selling replacement parts since the amount of expertise in the User Community is not available. ????????

Made a good income for me until I was no longer able to participate, so I'm not complaining just offering a possible explanation.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[stroupaloop]

Yes that's very true. I suppose that there is a mischevious outlining force of keeping the capital to the few people that do know the knowledge. I'm not sure if anyone or group of people will have the tenacity to establish an institute to develop such training...

I'm not sure how much more contamination control I should discuss on here considering that I'm not sure many could respond to such questions outside what they see/told by the manufacturer...

 

[IceStationZebra]

In my experience with the off-road industry the norm is a return filter of 10-40 micron, depending on the valve type and the normal environmental conditions.

Most machines have ~100 micron inlet strainer, but not always. The problem is excessive inlet vacuum during extreme cold start-up. The strainer is only used to keep trash and errant fasteners out of the pump.

With regards to ISO particle counts, most people don't care as long as the machine still functions. There is a little more attention to efficiency now with the high fuel prices, but most people don't understand the standby pressure is wasted heat for the most part! The one industry that I have experience with, that cares about efficiency, is the warehouse forklifts - but this is because many of the equipment managers compare fuel usage and will make future buying decisions based on it.

ISZ

 

[stroupaloop]

You're right ISZ. There is still a long road for a complete understanding of contamination control within the Fluid Power industry. It is hard press to get an industry that has few trained and knowledgeable engineers to even start thinking about designing a system for reliability.

Additionally, different applications require different filtration. Varying from the types of valves you are using, the type of environment, etc. justifies various filtration processes.

Your comment on the excessive inlet vacuum during extrame cold start-up is something I've ran across many times. I was on a consulting job up North and they were running trucking operations in such cold conditions that the viscosity of fluid was literally off the charts and would run out of a tube but fall very very slowly. Needless to say, this caused suction issues, creating a metal to metal grinding on their vane pump. An easy 5 minute idle time for their truckers was the trick...being patient of all things.

It is sad how people don't know or don't care about cleanliness, but somewhere down the distant future when people actually undersand fluid power, all their focus will be on reliability.

 

[hydromech]

Slightly off course...

On the subject of cold weather systems...has anyone had first hand experience of thermal shock?

On the subject of designing a system for reliability, well that depends on your point of view.

As a seller, the boss of the company wants bigger profits. He can either get that money by installing two micron filters and getting sales from replacement elements every 2 weeks and having the kudos of seeing the system running with fewer faults. Or he can go for the quick buck by installing a less effective filtration systems and selling a new pump every 12 months.

The difference is the cost of 2 micron elements against a high spec piston pump.

End users are, for the most part, ignorant of the benfits of contamination control and usually remove elements in the belief that they clogg and make the system slower.

OEMs that employ their own hydraulics systems engineers get the best of both and the pay the engineer crappy money so they are very well off.

I have worked on big open die forging presses with Towler valves that have had most of the valve block eroded by water and debris. I have also worked on and designed servo systems on flight simulators that were so clean we had to wear hair nets to service the power units.

It all comes down to...

1) CASH
2) EDUCATION
3) BEING BOTHERED TO DO IT PROPERLY.

Too few of us are educated about the benefits are good contamination control and everyone else will only be bothered if they start to lose cash.

Adrian

 

[stroupaloop]

It is true, many are ignorant of contamination control, but it always does come down to money...

Well I still consider negative thermal effects on a hydraulic system to be a merit for discussion of Contamination Control. From what I've seen out in the field, thermal shock usually creates issues due to material selection.

For instance, if all materials used had the same thermal expansion coefficients then a uniform change would occur, allowing for adequate free motion as temepratures quickly increased or decreased. However this is never the case.

Most noteably is seen within pumps. I've seen results of very hot fluid entering a cold pump, causing complete seizure due to the quick deformation of the materials expanding and creating interfacing contact between the open moving parts. Additionally, there was another instance where a pump was at low speed and high pressure, which generated high internal loses, creating very high outlet pressure. This effect burnt up the pump and greatly reduced the volumetric efficiency.

 

[hydromech]

It never get that cold in the UK for it to make enough difference.

I have seen it up in Alaska on a ship. A winch motor at a very low temperature had its casing flooded very quicky with hot, not warm, hot flushing oil to "gently" warm it up before running it.

It's funny how cold cast iron can act like glass when it comes into contact with hot fluid.

I said that to the ships chief engineer but he did not see funny side.