We launched our new website only a couple of months ago and I am thrilled with the traffic and response we are getting.
I am continuing to add more and more hydraulic content and intend to make this the largest hydraulic website available and help those with hydraulic problems, involved with dsign or are trying to learn more about the subject.
Those that have not visited the site please give it a try for Free!
Check out www.hydraulicbrain.com
All your comments are very welcome.
Thanks
Bob
Thursday, 21 July 2011
Why Rams Creep
So often I come across the problem of rams that creep out and this can be due to a few reasons.
Using a control valve with a centre position of all ports blocked is the most common cause. With this valve the blanked P port is under pressure and some leakage will pass either side to A&B, this will extend by displacing the rod area.
Another cause can be temperature. When the ram is locked in position using PO check valves or ball valves any temperature rise in the oil will cause expansion. If the piston seal is not 100% leak free the ram will creep forward. Without piston leakage the pressure could rise to an alarming value and cause damage to the ram.
Any load on a ram will make it creep over time. All valves have metal to metal sealing and the oil is the source of lubrication and leakage. As the running parts wear the leakage will increase and the ram will creep even more.
Always best to design with leakage in mind.
Cheers
Bob
More hydraulic stuff on www.hydraulicbrain.com
Using a control valve with a centre position of all ports blocked is the most common cause. With this valve the blanked P port is under pressure and some leakage will pass either side to A&B, this will extend by displacing the rod area.
Another cause can be temperature. When the ram is locked in position using PO check valves or ball valves any temperature rise in the oil will cause expansion. If the piston seal is not 100% leak free the ram will creep forward. Without piston leakage the pressure could rise to an alarming value and cause damage to the ram.
Any load on a ram will make it creep over time. All valves have metal to metal sealing and the oil is the source of lubrication and leakage. As the running parts wear the leakage will increase and the ram will creep even more.
Always best to design with leakage in mind.
Cheers
Bob
More hydraulic stuff on www.hydraulicbrain.com
Sunday, 10 July 2011
Quick release couplings
Quick Release Couplings can be extremely useful for applications where you are frequently connecting and disconnecting hoses; however they can also present some serious problems.
I have experienced occasion ions where the coupling has become worn or damaged (often by being thrown about on the floor) and will either only partially open or in the worst case will not open at all.
These couplings rely on a mechanical valve being forced open when pushed together. By their nature they often have a high pressure drop and also are an ideal source for dirt and contaminant to enter the system.
There have even been occasions on some systems when they become hydraulically locked and will not open.
I have nothing personal against quick release couplings, all I say is use them only where absolutely necessary, protect them from damage and keep them scrupulously clean.
Very best
Bob
www.hydraulicbrain.com
I have experienced occasion ions where the coupling has become worn or damaged (often by being thrown about on the floor) and will either only partially open or in the worst case will not open at all.
These couplings rely on a mechanical valve being forced open when pushed together. By their nature they often have a high pressure drop and also are an ideal source for dirt and contaminant to enter the system.
There have even been occasions on some systems when they become hydraulically locked and will not open.
I have nothing personal against quick release couplings, all I say is use them only where absolutely necessary, protect them from damage and keep them scrupulously clean.
Very best
Bob
www.hydraulicbrain.com
Sunday, 26 June 2011
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
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
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
Friday, 24 June 2011
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
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
Monday, 20 June 2011
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
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
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