Terminally sick systems

Over the years I have been called out to resolve a variety of hydraulic problems but there are some I call the terminally sick system or TSS for short. These are the systems that have gone unnoticed and uncared for that suddenly become mad, panic important because after the many years of abuse and unnoticed service they have finally decided to stop working.
The outside condition will often give the first clue to a TSS. It will be covered in a mixture of blackened oily deposits that has solidified over the years resembling greasy mud. When you look into the tank you recoil from the rancid smell of burnt oil and the colour has no resemblance to the once golden honey colour that was poured in from a new can. On taking a small sample of this gloop you hold it to the light and see a myriad of sparkling metallic particles and now you are convinced that you are dealing with a terminally sick system.
The customer is in panic because he cannot operate his machine and he will have to send everyone home if he can’t get it running within 24 hours and he has called you out because you are the expert and wants it fixed within the next few hours.
Yes, I have made up this story but it is not untypical of the type of breakdowns we are sometimes called out to resolve.
I have my own way of dealing with the TSS but I am more interested in how you would deal with this hydraulic emergency.
Very best
Bob
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Have hydraulic manufacturers become too arrogant?

I am sure that most of you will agree that getting new business and maintaining the existing is something that requires continued hard work. Most of the smaller businesses pay particular attention to giving good services and value their customers. I wish however I could say the same for the large manufacturers of hydraulic equipment. I am not sure if it would be a good idea to name and shame these companies but I guess that you might have a good idea of the ones I refer to.
I have some customers who buy branded products from me rather than deal direct. Not because I can save them money, in fact it’s likely it cost them more. It’s because they do not like dealing with the arrogant attitude so often associated with buying the parts they want. Comments like “You want it now, you must be joking, well if you don’t like 21 weeks delivery you can always go somewhere else!”
I notice that some of these companies do not even want to speak to us anymore. They hide behind a website with no means of contact other than an email address that they never reply to and finding a telephone number can take endless searching. I have been told by distributers that they also find it very difficult.
I rang a top brand servo manufacture for the name of someone who I could contact; I was told that the companies' policy was not to give out any names and that if I wanted I could send an email. The next time their rep knocks on my door or rings me up for an appointment you can guess what I will say to them!
We spend a great deal of time, effort and money trying to create a great experience for our customers as I am sure you guys do. We want our businesses to grow and be successful but some of these big companies have lost their desire or ability to give good service. Unfortunately for us we often have no choice but to continue to buy from them.
If you have had any experiences like me or disagree with my analysis I would love to hear from you.
Cheers
Bob

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Piston Rods

The piston rod is the key component to any hydraulic ram and probably the most prone to damage.
The rod must be the right length and diameter to avoid buckling and strong enough to take the load.
What I wish to focus on is the surface finish.
Many rods are made from high grade carbon steel and flash chromed. Often you can buy the material straight off the shelf and ready to machine the ends.
The chrome is used for its hardness and wear ability. Under the microscope it will appear like a crazed plate and if subject to a prolonged wet environment the chrome will soon show signs of rust and bubbling up of the plated surface.
On marine applications I once used stainless steel with chrome on top. The stainless was soft but corrosion resistant while the chrome is hard and porous. A great combination you might think. After a few months we discovered tiny marks in the chrome. Under a glass it appeared like a small crater with a very sharp edge.
The chrome was being pulled from the rod and we put this down to the electrolytic action of the seawater. We installed a sacrificial anode with little improvement. Eventually we replaced the rods with plain stainless steel. We suffer a little extra wear but keep the seals in good order.
Also do not make your rods with a too perfect finish. High polished rods will wear the seals due to reduced lubrication.
There are lots of other interesting things about piston rods but I just thought of a couple but please tell us about your experiences.
Cheers
Bob
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Grooves in Pistons

I was recommended a book “Hydraulic Control Systems” by Herbert E Merritt. Although the maths flies gently over my head there is some very interesting stuff for the Hydraulic enthusiast.
I recently asked a question about grooves in pump pistons and valve spools and what was their purpose. I found the answer and I will try to explain in my own Layman’s language.
With close tolerance pistons it is possible for hydraulic forces to create lateral movement on the piston forcing it to one side of the bore. This can cause stiction (hydraulic lock), extra leakage and a trap for contamination.
Just one groove on the piston can reduce the lateral forces by up to 40%. The grooves create a centreing effect and help prevent metal to metal contact between piston and bore. Adding more grooves will also be beneficial.
The depth and the width of the groove should be 10 times the clearance and the sides of the groove should be perpendicular to the bore.
Ref from Hydraulic Control Systems

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Things you remember

Anyone with a long career in hydraulics, I am sure will remember those times when things went badly wrong and ended with a few sleepless nights. The one etched in my distant memory was an application for a hydraulic riveting system. The client need several pressures all quite set close to each other. On the face of it a very simple straightforward project. We tested the system in the workshop and all seemed well before delivering it to the customers factory.
Within a few days we had the first of many phone calls.
It seemed that without warning the system started screaming so loud that the workers had to cover their ears.
By the end of the week the power pack was back. We tried all sorts of things to resolve the problem and each thing we tried we thought it was fixed, only to discover that within a few days it would start playing up again with the ear shattering noise.
In the end we admitted defeat and re reimbursed the client in full.
For me, at the beginning of my hydraulic career it was a huge blow and I considered that maybe I was not cut out for a future in hydraulics.
But you eventually move on and get bad experiences behind you with more successful jobs. However when I come across an application with two Relief valves in the same circuit I feel that familiar sickness again envelope my being.
Regards
Bob

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What is Regen?

Regenerative (Regen):
This often causes a little confusion with newcomers to hydraulics and I hope that I can make it easy to understand. We use the Regen circuit when we need a fast extend e.g approach cycle on a machine tool. Very simply, when extending we only displace the rod volume not the cylinder volume.
This means that the rod will move out faster but will have a much reduced force due to its area.
When we reach the point where we need the large force then we can switch out the Regen and apply pressure over the whole piston area. The ram will now move slower but we only need force not speed. Regen can only work on the extend stroke, however the ram will return quickly due to the anular area. 
Be careful! with too large a rod the benefits may not be worth while. If rods are too small the force may not be large enough to overcome seal friction.      
Bob
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The Pump Coupling

In my early apprenticeship days a common task was to fit the pump to the motor. A simple task I hear you say. In those days it could take several hours because the motor and pump were bolted onto machined pads and had to be shimmed to get the coupling spot on line. The coupling had 4 rubber covered pins that were inserted into the mating half that had to have a small amount of movement. Our key fitting skills were also put to the test using micrometer blue to ensure a good fit.
One day we were given a different type of coupling called a “Taperloc”. It was so easy to fit and did not rely on the great accuracy and filing skills.
Since those days couplings have become easier to fit and Bell housings make it simple and more reliable.
There are still areas where we need to take care. Most pumps do not like Belt drives because the front bearing is not fit for the heavy side loading. However you can obtain easy use bearing units that fit neatly onto the pump.
I have had a pump shaft spline fail on motor a of 200Kw and created vibrations so severe that a structural engineers was called in to examine the building for damage.
Couplings are extremely important and often we tend to give them second thought.
Bob
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