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!
Thursday 24 February 2011
Pump Strainers
Those for Strainers, would claim that they prevent large particles from entering the pump via the suction pipe and anything large will almost certainly wreck the pump. A big piston pump could cost thousands of pounds.
Those against would say that strainers are 125micron and do not stop small particles. They also collect silt and fiberous material on the mesh which eventually blocks the strainer and damages the pump through cavitation. Strainers are located in the tank and owners are not always aware they exist. By the time they do, the pump can be wrecked.
Those against would say that strainers are 125micron and do not stop small particles. They also collect silt and fiberous material on the mesh which eventually blocks the strainer and damages the pump through cavitation. Strainers are located in the tank and owners are not always aware they exist. By the time they do, the pump can be wrecked.
Synchronise Rams
Synchronise Rams
Over the years I have seen many methods used to synchronise hydraulic rams, some successful and some bordering on the bazaar.
Getting rams to move together can be tricky and applications like “ A frame” cranes can be potentially dangerous if the wrong method is used.
The simplest method is to join rams together using a mechanical strut / beam that is strong enough to take any out of balance forces. We often see rams used this way on Skip Lorries where the two rams are joined together with a cross beam and the input flow split using just equal lengths of pipe work.
More accurate control can be effective with flow divider valves, gear and piston motor types. These offer more better control with accuracy between 5-10% of stroke but as wear increases these figures will also increase.
The most accurate form of synchronisation will be achieved using a servo closed loop control with linear transducer feedback. One cylinder will be driven whilst the other slaved.
I have also used NC valves with stepper motor control. Using one digital input signal to two stepper motors that drive the NC valves. This has its own inbuilt mechanical feedback mechanism that can synchronise rams to just a few microns even with an off centre load.
Over the years I have seen many methods used to synchronise hydraulic rams, some successful and some bordering on the bazaar.
Getting rams to move together can be tricky and applications like “ A frame” cranes can be potentially dangerous if the wrong method is used.
The simplest method is to join rams together using a mechanical strut / beam that is strong enough to take any out of balance forces. We often see rams used this way on Skip Lorries where the two rams are joined together with a cross beam and the input flow split using just equal lengths of pipe work.
More accurate control can be effective with flow divider valves, gear and piston motor types. These offer more better control with accuracy between 5-10% of stroke but as wear increases these figures will also increase.
The most accurate form of synchronisation will be achieved using a servo closed loop control with linear transducer feedback. One cylinder will be driven whilst the other slaved.
I have also used NC valves with stepper motor control. Using one digital input signal to two stepper motors that drive the NC valves. This has its own inbuilt mechanical feedback mechanism that can synchronise rams to just a few microns even with an off centre load.
Should you paint inside the tank
Should the inside of the tank/reservoir be painted or left bare?
This is a question I am often asked.
Leaving the tank bare risks the build up of rust and this can drop off and contaminate the oil.
Painting the tank with a good epoxy has benifits including.
1) It will seal in particles missed from cleaning (bits of weld splatter)
2) Prevents rust building up.
The issue I have with painting is if comes off (big problem!)
I have seen tanks where the lids and the sides have been painted only down to the oil line.
This is a question I am often asked.
Leaving the tank bare risks the build up of rust and this can drop off and contaminate the oil.
Painting the tank with a good epoxy has benifits including.
1) It will seal in particles missed from cleaning (bits of weld splatter)
2) Prevents rust building up.
The issue I have with painting is if comes off (big problem!)
I have seen tanks where the lids and the sides have been painted only down to the oil line.
Holding a Load
A problem that raises its head every so often is holding a load on a ram.
I don’t mean for a few minutes or even an hour I am talking about many hours or even days.
Holding a load for a short time can easily be done using a pilot operated check valve. This is probably the best valve because being a seated poppet they are less likely to leak although a little contamination under the seat can cause a problem.
On occasions I have been asked to close the ram off with ball valve, which I refuse to do.
Any leak across the piston can cause pressure intensification due to the ratio of the piston and rod area.
As far as I know there is no way of holding a load on a ram for long periods of time and it should be no surprise to raise a load one day only to see it down the next unless a mechanical locking mechanism is used.
I would like your views, maybe someone out there has other interesting ideas they can share.
Cheers
Bob
I don’t mean for a few minutes or even an hour I am talking about many hours or even days.
Holding a load for a short time can easily be done using a pilot operated check valve. This is probably the best valve because being a seated poppet they are less likely to leak although a little contamination under the seat can cause a problem.
On occasions I have been asked to close the ram off with ball valve, which I refuse to do.
Any leak across the piston can cause pressure intensification due to the ratio of the piston and rod area.
As far as I know there is no way of holding a load on a ram for long periods of time and it should be no surprise to raise a load one day only to see it down the next unless a mechanical locking mechanism is used.
I would like your views, maybe someone out there has other interesting ideas they can share.
Cheers
Bob
Thursday 10 February 2011
I was kindly sent this by Sampathkumar Iyengar showing a filter screen in a hydraulic tank. I have never seen this done before. Looks a very good idea!
Many thanks Sampathkumar
Dear Bob,
These screens serve the purpose of filtration of oil from the dirty side to the clean side of the reservoir.
These screens can be periodically removed for cleaning and re inserted in the slots.
These screens have advantage of large area of wire mesh available to trap dirt and debris from the return line of systems
For the suppression of bubbles we weld a sheet with a 45 degree slope with perforations on the side leading to the clean chamber
I am enclosing an additional photos with remarks for clarity.
Trust the information assists
Best regards
Sampathkumar Iyengar
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