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Posts tagged: hydraulic filter

How The ISO Guide to Hydraulic Filter Performance Works

ISO — the International Organization for Standardization — releases guides for almost every conceivable area of industry on Earth. Some of these are easy to understand, others are packed into language so dense and jargon-filled that it takes an industry expert just to read the introduction. We thought we’d shed a little light on hydraulic filters for everyone by unpacking the ISO codes for cleanliness, which are used for virtually every kind of air and/or liquid filter, including hydraulic ones.


How Small is a Micron?

The core unit by which the ISO measures ‘uncleanliness’ is the micron, which is a measure of distance. Filters are measured by how many particles of what diameter (in microns) they allow through. But before we get into that, let’s talk about what a micron is. Unfortunately, they’re so small, we have to describe them, because simply telling you “one millionth of a meter” doesn’t have any meaning. So here are three quick examples to help you understand:

  • The average human hair is about 70 microns wide.
  • A single grain of standardized table salt is about 120 microns wide.
  • The eye of a standard American sewing needle is a whopping 1,230 microns across.


Particulate in Microns

The ISO standards for particulate break them down into three categories:

  • 4 microns and smaller (about the size of a larger bacterium)
  • 5-6 microns (about the size of a deoxygenated red blood cell)
  • 7-14 microns (about the size of a mold spore)


Presumably, particulate larger than that only gets through a filter if that filter is critically compromised.


The Confusing World of ISO Codes

The ISO tests a filter, and they assign one code for each of those categories, in a string like this: 20/17/14. The ISO code is, unfortunately, not intuitive. In short, an ISO code of ’10’ means ’10 or less of this size of particle per milliliter of volume (after filtration).’  Every number you go up from 10 doubles the “X or less” number; every number you go down from 10 halves it.



So when you see a hydraulic filter with a three-digit rating like 32/12/4, you can look at it and say to yourself “OK, so after the fluid has been filtered, it’s got about 32 bacteria, 12 blood cells, and 4 mold spores in it.” Of course, what those particles actually are is often more important than the size (if they’re aluminum, you’ve got significantly greater problems than if they’re water — but that’s a different post altogether.




Two Kinds of Hydraulic Manifolds, Part II: Modular Manifolds

In Part I, we discussed the benefits of one of the two major types of hydraulic manifolds — the ‘single-piece’ manfolds, laminar and drilled-block. Today, we’re going to talk about the other major kind of manifold: the ‘modular’ manifold.

Modular manifolds have a single massive advantage over single-piece manifolds: they can be changed on the fly as the job evolves. Sometimes called the ‘erector set approach,’ modular manifolds involves a few to scores of iron, steel, or aluminum blocks, each of which has a single valve or other operator inside. Modular manifold systems can be assembled horizontally or stacked.

Most often, plates are installed between the basic ‘building block’ components to make for regular spacing and to allow for small variations in the location and size of intake and outflow passages.

The method by which the manifold blocks are connected varies by builder. Some use rods that extend through the length of the manifold and are secured on either end with nuts. Others have flanges on every block so they can be bolted together one at a time. Still others have sockets and threaded heads alongside the hydraulic passages inside each block that snap together. No matter how the blocks are connected, every block has an O-ring around every passage entering or exiting it that abuts the O-ring on the adjacent block for the purpose of forming a seal.

Most such blocks also have the necessary electrical connections built into the blocks, connecting the machinery to the appropriate solenoid. Some instead utilize channels that allow for runs of standard electric cable instead.

The limitations of modular manifolds are more dramatic than those of single-block manifolds. Internal pressure, flow rate, and the length of an individual manifold are all much more sensitive in a modular manifold than they are in a single-piece manifold.

Hydraulic manifolds are amazing tools, able to replace as much as 300 lbs of tubing and valves in as little as a single cubic foot of space. Compared to the tubing and valve setup, a manifold can cost two-thirds to half as much to assemble and install, save a mountain of space, and require only a single hydraulic filter to keep the fluid running smoothly. Whether you choose drilled-block, laminar, or modular manifolds, you’re certain to appreciate the advantages.

Hydraulic Pumps: Fixed vs. Variable Displacement

A hydraulic drive system uses a pressurized fluid to deliver force to distant machinery. Each system has several common components; the most universal is the hydraulic pump. The pump’s purpose is to pressurize the hydraulic fluid so that it will travel down the line and perform work on the other side. In an ‘open loop’ system, the fluid is drawn from a reserve tank, and deposited into the same tank after it has done its work. In a ‘closed loop’ system, the fluid is brought directly back to the hydraulic pump after passing through a hydraulic filter.

Fixed Displacement Pumps
A fixed-displacement pump has a set flow rate — every stroke of the motor moves the same amount of fluid. Fixed-displacement pumps are

  • Simple
  • Relatively inexpensive
  • Easier to maintain

The simplest type of fixed-displacement pump is the gear pump, in which the hydraulic fluid is pushed by rotating gears. In some models, the gears are sequential; in the quieter and more efficient version, the gears are interlocking. Another common variation is the screw pump, which uses the classic Archimedes screw, which looks much like a drill bit, to move the fluid. They have the advantage of providing a high rate of flow at relatively low pressures.

Variable Displacement Pumps
In a variable-displacement pump, the flow rate and outlet pressure can be changed as the pump operates. This results in pumps that are

  • More complex
  • More expensive
  • Capable of doing a wider variety of jobs

The most common type of variable-displacement pump is the rotary vane pump, which is a variation of the gear pump in which the ‘gear’ is offset and the ‘cogs’ aren’t fixed, but rather extend and retract as the gear turns, allowing the pump to increase the pressure of the fluid by compacting it as it pushes the fluid through. The top-tier pumps, however, are bent-axis piston-and-cylinder pumps, much like the ones that are used in an internal combustion engine.

Simple, fixed-displacement pumps are perfect for single jobs that need to be repeated indefinitely over long periods of time; variable-displacement pumps can be used to power a wider variety of tools, but require more expense and more attention.

What Does My Hydraulic Filter Do?

Hydraulic fluid has a number of purposes inside of a hydraulic system. In addition to it’s obvious purpose of transferring force from a hydraulic power unit to an actuator, it has a few less-obvious purposes as well:

  • It helps to seal the hydraulic system through the power of surface tension and adhesion,
  • It lubricates the system by preventing metal surfaces from contacting each other,
  • And it helps balance the temperature of the system by transferring heat from one area to another.

If any of these functions are compromised, the entire system can become compromised. The obvious question, then, is ‘what causes these functions to become compromised and how can we prevent that?’ As it turns out, the most common cause of compromised hydraulic fluid is particulate that builds up in the fluid.

Particulate build-up might not cause the force-transferring properties of the hydraulic fluid to dissipate, but all three of the other functions are vulnerable to particles. They breach the surface tension of the fluid, breaking the ‘seal’ that the fluid forms that prevent microscopic leaks from becoming problematic. They can get pinched between metal surfaces that would otherwise have been adequately lubricated and cause damage to those surfaces. And by causing excess friction, they can overcome the ability of the fluid to keep the system cool.

The way to prevent particulate build up, as you may have guessed, is to use and regularly change your hydraulic filter. A hydraulic filter eliminates particulate contamination, which in turn prevents a goodly number of the problems that can crop up within your hydraulic fluid.

What Won’t My Hydraulic Filter Do?
The hydraulic filter isn’t the be-all and end-all of hydraulic system maintenance, however. No filter can keep water entirely out of your hydraulic fluid, for example, and water has a variety of negative effects on the system. Furthermore, the particulate that gets into your fluid comes from the inside of the parts of your hydraulic system — microscopic chunks that break off. Given long enough, that wear can affect the performance of a part, which will need replacing.

That said, nothing is quite as cost-effective at increasing the functional lifespan of a hydraulic system like regular replacement of the hydraulic filter — so make sure you stay on top of it!

Form Meets Function: The Hydraulic Filter At Work

Hydraulic fluids have four basic purposes. First, they create force and motion by taking pressure from one place and moving it flawlessly to another place. Second, the fluid acts as a kind of seal, helping to keep contaminants out of the system by virtue of filling all of the available internal spaces and having surface tension. Third, the fluid acts as a kind of lubricant, and finally, it helps keep the hydraulic system cool as well.

Of course, it’s not perfect at any of these jobs — and when the second purpose fails and contaminants get into the system, everything else gets worse along the way. That’s why no hydraulic pump system relies entirely on the fluid itself to keep contaminants out — they inevitably also use a hydraulic filter.

Getting Contaminated
Contaminants come from a few places:

  • They can be sealed into the system when the system is first created or when new fluid or parts are added.
  • They can come from inside the system when microscopic particulate is broken off of the existing parts and pieces.
  • They can get into the system from outside during normal operation. Breather caps, imperfect seals, and basically any opening that exposes the hydraulic fluid to the air (deliberately or not) can cause contamination.

How Big Does A Particle Have To Be to Cause Problems?
To be honest, it depends — some particulate has chemical, rather than mechanical, interactions with the internals of a hydraulic system, and that kind of particulate — say, rust — isn’t safe in any quantity. But the more common, sand-like particulate can get as “large” as one ten millionth of an inch before it starts causing problems in today’s modern electrohydraulic devices. Yeah, that’s really really small.

What Problems Do Particles Cause?
Diminished system performance. Shorter component life. Reduced flow rate or increased slippage as abrasions degrade internal clearance dimensions. Catastrophic failure, at the worst end.

How To Prevent All This
It’s simple: make sure you have a good hydraulic filter built into your system, and change it regularly to make sure it stays maximally effective.

Save Space and Time With a Hydraulic Manifold

Hydraulic manifolds are powerful and compact valve assemblies that do for hydraulics very much what integrated circuits do for computers: they create a system where a relatively simple set of hydraulic inputs can be used to create a startling array of hydraulic outputs. The end result is a single smallish chunk of machinery that replaces hundreds of feet of tubing, hose, fittings, and line-mounted valves. While hydraulics still use liquid rather than electrons – and thus a hydraulic manifold will never reach the staggeringly small size of a modern integrated circuit – they do squeeze a huge amount of functionality into a very small space.

That’s not the only advantage to a hydraulic manifold, however: there’s also the issue of leakage. That aforementioned hundreds of feet of tubing, valves, hose, and fittings means scores of individual parts each one of which can go wrong and cause a leak (which is a death sentence for a hydraulic machine). Hydraulic manifolds are prebuilt out of as few parts as possible for the various valves to do their jobs, and that means significantly less opportunity for leaking (and correspondingly less need to spend time and labor on fixing the leaks.)

Hydraulic manifolds also require less assembly, which means easier maintenance and troubleshooting, which again saves money on the project’s bottom line. With so many components built into or mounted upon a single common manifold, the need for a tech to climb all over Kingdom Come to find the leaky piece is dramatically reduced. Should the hydraulic manifold itself fail, there are dozens of identical units – swapping one out is the job of less than an hour, and that’s in poor circumstances. Furthermore, oftentimes the faulty manifold can be repaired on the spot and kept en situ as a swap-in replacement should something happen to the manifold that was just installed.

Modern hydraulic manifolds also provide advanced capabilities like load sensing, which allows the manifold itself to detect how much pressure is needed to lift a certain load and provide exactly as much as is needed, conserving hydraulic power to direct elsewhere for other jobs. Some such manifolds even have a hydraulic filter built into them so as to further reduce technician’s walking time. When everything is in one place, you waste a lot less time getting from wherever you are to where the problem is.