Pipe-work and Hoses

When I first started out in hydraulics, hoses were as rare as hen’s teeth.
My apprenticeship gave me many skills and the opportunity to discover various disciplines including the pipe fitting.
We bent and manipulated pipes of all sizes, including filling some pipes with sand to prevent them collapsing.
One day we were given hoses to fit and told that they were suitable for high pressure and could flex and bend, unlike steel.
Nowadays things are very different, hoses are no longer fitted just because they can bend. They are mostly fitted because of quickness and cost.
But are they better?
Steel pipe-work is often fitted for life, where hoses have a much shorter life and will need replacing. Personally I love to see well fitted steel pipe-work, it looks smart and is an integral part of the machine. Hoses often look like bird’s nests, untidy and tide on. The other day I was working on a mobile machine where I had to track the pipe-work, it was a nightmare trying to leaver the hoses apart.
Some systems require “stiffness” to provide good accuracy and steel pipe is better, however hose can provide compliance and help reduce noise and hydraulic shock.
I have no doubt that hoses have their rightful place but I also believe that we should be more discriminate and not just fit a hose because it is quick, easy to fit and cheap.
If you have views I would love to hear from you.
Cheers
Bob

Po check or Counterbalance

The Pilot Operated Check and Counterbalance valve are not only different in construction they are also different in their use.
The POC is a normally closed valve that is primarily used for holding a load. It is a poppet valve held down onto a seat by a spring. The valve can be lifted off its seat by a small piston and the pilot pressure created in the in- put leg of the circuit. Like all check valves they can be sharp acting and unstable if fitted inappropriately.

The Counterbalance valve is a spool valve normally closed and piloted to open by pressure in the in- put leg of the circuit to the actuator. The big difference is that the valve will modulate (move back and forth), open or close in proportion to the pilot pressure. This valve is designed to stop the load running away. If the load tries to move ahead of the input flow to the actuator, the pilot pressure will reduce and restrict the output flow thus checking the speed.
Also the valve has an added feature of a relief valve that will prevent over pressure.
Comparing the POC with Counterbalance, the latter is far more controlled with a much smoother operation but I have found them to be more susceptible to failure than the POC and can often render a situation with a load stranded in the air.
Over the years I have experimented and replaced the CBV with a POC. To provide the same effect it is also important to install a relief valve on the holding side (Pressure to tank) and a flow control to stop the load from racing away ahead of the input flow. The only downside with this set up is that there is the danger of the relief valve failing open and it is not ideal for a varying load unless you use a pressure compensated flow control valve. Otherwise I found the system to be more reliable and less prone to leaking. This is not suitable for all applications (where maximum safety is required) but can have its place for some applications. Imagine where it is crucial that the actuator must not get stuck in a dangerous position.
If you have used these valves in a more unusual way or different setup or have comments regarding this subject I would be pleased to hear from you.
Cheers
Bob

Protecting Cylinder Rods

I have just been reading an online article/blog claiming the benefits of using shrouds and bellows to protect hydraulic cylinder rods. We moved away from this method of protection many years ago.
It became very obvious to us that shrouds and bellows created more problems than they solved.
As the bellows extend and retract they must be able to breathe often through small filters to stop contamination entering. These small filters can easily block with the result of damaged bellows. Now it will be possible for contaminated air to enter and debris can build up creating a compacted solid mass and held in place by the bellows. This can cause considerable damage to the rod, the very thing you were trying to prevent.
Our conclusion is, do not use bellows as they make the situation worse.
You may have a different view that I will be pleased to hear

Pipe-work v Manifold

It can be a difficult to choose between using pipe mounted valves or design and installing a manifold. There are benefits and disadvantages to both systems and here are a few.
Pipe-work (benefits)
1) Can be modified easily
2) Fault finding easier
3) Dissipates heat
Manifold block (benefits)
1) Compact and tidy
2) Fewer leaks
3) Quick and less installation skill required

When I fault find a hydraulic system it always becomes a lot more difficult with a manifold.
You cannot get in and isolate valves or test individual valves. Prototype systems often need some modifications and again the manifold can be more difficult.
Leaking pipe fittings can be a big problem with pipe-mounted valves and the more valves the more fittings and leaks.
I think that the manifold block is very much like the modern car. It’s great when everything is working well but difficult when things go wrong.
If you have some views I will be pleased to hear

Cheers
Bob

The Future for Hydraulic Drives

It did not seem that long ago when I first came across a company selling a device called an inverter.
They told me that is was possible to take a standard 3 phase electric motor and vary the speed.
This was something up until then that you could only do with a hydraulic drive. Well the rest you will say, is history. We now see electrical drives of all sizes driven this way. Not only speed but torque control also.
Over recent years we have seen more and more electrical drives replace hydraulic drives. Where once a hydraulic drive was the only sensible solution there now sits a sparkling, clean, leak-free, efficient electric motor.
The only places I now see hydraulic drives now are mainly, marine and mobile applications or where power to size ratio is important.
Also electrical drives are more efficient and have considerable power savings with smoother control.
What does the future hold?
Is there an electrical linear drive around the corner that can compete with hydraulic rams, if so what is the future for Hydraulics systems?
Regards
Bob

The Law of Diminishing Returns

I have been designing systems for many years and like any Hydraulic System Designer
I try to cover every possible scenario.
We look at what might/ could happen that could affect safety of the operator or cause damage to the equipment.
Maybe you are concerned about what happens if you get a power failure or maybe an external force reacting back on the ram. It might be an event that is very unlikely to occur and you wonder if to cover it in the design or because it’s such a very rare event, take the chance!
What I am getting at here is about the sleepless nights and the myriad of extra valves you use in order to safeguard against all of those possibilities.
You then take another look at your system, it is bristling with valves and resembles an over decorated Christmas tree. You now worry that you have created a system with a greater risk of failure because of the number of parts and what about all that leakage!
We have the saying “Keep it simple stupid” kiss, but at what point do we draw the line and say we have gone far enough without compromising safety?

Changes over 45 years

I,ve been in hydraulics for over 45years and watched the industry off- load their technical sales people. We are now referred to websites to sort it out for ourselves, is this the way forward?
Sound technical product knowledge seems to be something of the past. Many sales engineers, with years of experience could offer good advice on how you could use their product. They new how much extra margine you might have on pressure or flow etc.
With few exceptions, you are now passed from pillar to post and usually end up on a website sorting it out for yourself and hoping that you have got it right.
There is nothing that gives more confidence than buying a product from an engineer who knows his stuff!