Hydraulics is Business

Some of the comments I read are to me like a fashion show. Great entertainment, interesting and above all, fun. But not something I would want to wear myself. Sometimes we stray away in our daydreams to the place of fantasy (not a bad thing). But speaking only for myself, I am in business and the bottom line for me is “can I make a profit”
Now I can hear many members yawning or crying Luddite! but I am sorry chaps but that is the end game for me however I am not sure I would be able to earn my money in any other more interesting way.
During my career I have worked for some very high profile hydraulic companies and been involved in R&D on important military projects. At one time I was the least qualified in an office of 10-12 everyone bar me had a PhD and the maths were eyewatering! These were engineers that became good friends and whom I had the highest respect for. But even they at times got it wrong and when they did they got it wrong big time!
When I started to work for myself I stuck to simple KISS. The bigger the system the simpler I made it. The more complicated the system I would let someone else take the glory. Getting it wrong costs me hard earned cash! and I am not in it for the academic journey.
I apologise if I have upset anyone with my simple and basic way of business and it might seem very boring to others and over nearly 50 years I am still learning the basics and still loads to learn about but for those more adventurous, Bon voyage.

www.hydraulicbrain.com

Hydraulics are so simple?

I once had a customer who told me that there was nothing difficult about hydraulics and it was pretty simple stuff and hinted that my work was over rated. I smiled and obviously could not agree because the fascination of “Fluid power” is that no matter how long you work in the business you NEVER stop learning. These forums prove that and are great value to me for picking up other people’s tips and experiences.
I will like to briefly tell you of an experience I had a couple of years ago.
I designed a small system for a “Super Yacht” to control the transom door that turns into a platform at the stern of the boat with two polished stainless steel rams . (Very expensive stuff!)
I purchased a small DC pack with pump. Motor, control valve and reservoir. When I operated the system it worked beautifully for just a short time and then stopped. I checked everything, control signal, valve, but could find nothing wrong. I drained the tank and checked the pump and everything was in order. It would start work for a few minutes and then stop.
3 days later I had changed the pump, valve, housing and electric motor and I still the same problem. I felt that I should take up a different career (so did my customer)
I decided to remove the tank for the 10th time and I sat there staring at the stripped down parts. I ran my hand around the empty tank pondering the problem almost in a dream like trance. Suddenly my hand felt something strange and my attention quickly snapped into curiosity. I carefully picked away a piece of polythene about 50 mm square a piece of left over packaging. This would stick to the side of the tank (undetected) when empty and gently float off and cover my suction port when filled with oil.
It was a “wake up call” never think you know everything!
www.hydraulicbrain.com

Decompression

With large rams you might need to consider decompression.
We know that oil compresses at around 0.5% of volume per 1000psi.
A large volume ram can have a considerable volume of compressed oil and when suddenly released through the control valve may cause a bit of a bang!
This can be reduced by a decompression valve that allows the pressure to bleed off more slowly before allowing the main valve to fully open.
Some Pilot operated check valves have this feature and some control valve spools have flats ground onto the leading edges.
I remember years ago when we needed to get ourselves out of trouble we would take the spool to the hand grinder. But best not mention this to anyone!
Very best
Bob

Changing the Pressure on a Machine

I was called out a few days ago to look at a tube bending machine.
The machine was PLC controlled and runs with a semi automatic program. The client has a problem bending a large steel pipe and asked if I could help. The machine was second hand with no manual so I had to quickly start from basics. The pressure was set to the highest value and the machine did not quite have the full force needed to complete the bend although it was just possible by switching the control valve off and back on again to achieve a pressure spike.
It would be possible to change the spring in the relief valve (to higher rating) but then the vane pump had a maximum of 140bar and the existing pressure is pretty close. Then there is the electric motor. By increasing the pressure we will need to draw more power and without knowing the flow and the motor Kw I could not calculate what my motor draw. Last of all I should also consider the mechanical strength of the machine. Will it take the extra load without breaking something?
Raising the pressure is a very easy thing to do but not before you have considered all of the implications.
Regards
Bob

New Linkedin forum

I have just launched on new forum on Linkedin.
The purpose of the group is to help and support each other on issues relating to Fluid Power.
Due to the platform used, where the only method of communication is print extra effort must be made to ensure that the message sent to the recipient and the group should appear friendly, helpful and positive to the discussion.
We hope to have fun, make good friends and learn about other members Fluid power experiences.
Please come and join us.

The name of our forum is "Hydraulic help"
Cheers
Bob

Controlling Speed

There are many ways to control the speed of a hydraulic ram or motor.
We could use a pump that delivers a variable flow (variable piston or vane pump)
The easiest way is to fit a flow control valve but the question comes where do you fit it?
Meter out: This is where a valve is fitted to each leg of the mover. The arrow for free flow should point towards the mover port. The flow is restricted on the return leg back to the control valve. This will prevent the load running ahead of the oil supply and keep the system stiff. However if screwed down too far can cause some intensification on the annular side of the ram.
Meter in: Good when the mover is pushing against a load but not if the load is trying to pull the ram. Imagine pushing a car up a hill. The best place to push is behind the car. As the car reaches the summit you need to move to the front to stop the car running away. The valve should be fitted with the free flow arrow pointing away from the mover towards the control valve.
Bleed off: This can be fitted on any leg of the mover or the main pressure line.
The valve is piped to tank and bleed oil off the main flow. This can be problematic and will not give a wide range of speed control. One main benefit is that it is less prone to generate heat.
Flow control on Pressure inlet: The valve would be a simple needle valve type.
Will cause heat generation. Excess oil will pass across the relief valve.
If you are unsure what is the best way for your system please send me an email.
I will write more on this subject including, pressure and temperature compensation and Load Sensing.
See more on www.hydraulicbrain.com
Cheers
Bob

One pump or two?

When a system requires more than one ram or motor the first question to ask is do they work at the same time. If they do you must now consider the implications. Using hand valves might just result in less speed but because oil always takes the least resistance it might stop one movement altogether.
If in doubt I prefer to use one pump for each device and then I am sure that one “mover” will not affect the other. It’s very difficult to put right if you get this wrong!
If you know a better and reliable way I would love to hear from you.
Cheers
Bob

Pump Design

I am sure pump designers would love to find ways to completely eliminate, Pressure drop across the pump (with free outlet) together with, friction, noise and heat. (wasted energy) but this is the price we pay to get the flow through the pump. These are the “undesirables” of pump design we must live with (due to physics) although with better design and technology we continue to improve.
Flow is the desirable product we want from the pump and it is important that we make the pump strong enough to resist any restriction of that flow up to a maximum design pressure. After that we will likely cause damage to the pump.
So how does the pressure change within the pump?
1) By increasing pump speed (increasing the flow)
2) Changing the oil (resisting flow)
3) Adding a load (resisting flow)
4) Pipe size (resisting the flow)
And so on..
With a load sensing pump we sense a change of pressure (due to change in load) across the control valve and the pump will automatically respond and make corrections to maintain Delta P. This pressure adjustment can only be achieved by adjusting the pump flow. .
This is why we say pumps produce flow not pressure but they are designed to take pressure

How would you define a pump?

How would you define a pump?
A very simple question you might think especially for a hydraulic professional.
This was the simple question posed by a young graduate on Linkedin. Over 3 months later with over 100 comments it is still being debated with some veracity.
I was always taught that pumps produce flow and pressure is a restriction of flow. A challenge to that view is that there must be a force or pressure to move any mass, therefore fluid being a mass means that if there is flow from a pump there must be pressure. I have to agree to this observation and is irrefutable.
So why don’t hydraulic people acknowledge this pressure when we know that there must be some pressure , no matter how small?.
Some things we are taught are often accepted without challenge because with a subject like hydraulics at the beginning one is trying to cope with the overall understanding without thinking of challenging the basics. These concepts eventually become accepted and fixed in one’s own mind until one day someone challenges that view.
I will give you my opinion why we ignore/deny that pumps produce pressure. I believe that by acknowledge this inbuilt load/pressure in our” definition of a pump” will it make the concept clearer or more confusing especially to those with little knowledge of the subject? I believe the latter but more than that what extra benefit does it provide to the hydraulic engineer? I suspect very little.
We know that pumps have different efficiency values. We acknowledge this in our pump power calculations. No pump is 100% and it will be reduced by friction in bearings, running gear and of course the energy needed to push the oil through the pump (also leakage). In hydraulics we factor this into our calculations and because it is a relatively small force value we often tend to ignore it. Remember that hydraulics is used to move or rotate very large loads and as a percentage of these loads the force to push the oil through the pump is very small indeed.
In future then, now that I have given more thought to this issue, how will I describe a pump? I will likely make some adjustments based on whom I am speaking to. Those starting out in hydraulic or struggling with very basic knowledge I will stick to “pumps provide flow” and for those that require a more precise definition: “A pump is a device that forces fluid through its mechanical parts to produce flow” This is wordier but I think a more accurate definition but not sure that it changes much!
Very best
Bob