I was asked to oversee the installation of a hydraulic winch system installed on a workboat and designed by (winch experts)
My client had used this company before and was very satisfied with their expertise and service. If my client was happy then so was I.
It came the day when I had to inspect the installation. There was a gear pump attached to a large diesel engine via a flexible coupling, the winch was fitted on deck and the control valve, counterbalance valve with manifold were supplied loose.
I studied the circuit and the first thing that caught my attention was the closed centre control valve. This prompted an immediate phone call to the designer, the last thing we wanted was a hot system. He assured me that the control valve supplied was in fact a Pressure to Tank configuration and that he had drawn the symbol incorrectly. I then asked him what speed had he designed the pump to run at, “1000rpm” he said.
Now under normal conditions whilst using the winch the engine speed would run at 1000rpm but when the boat steamed from one position to another the engine rpm can increase to 2100-2200rpm, more than twice the design speed and what is more important twice the design flow.
Now we have a problem!
The control valve and pipe-work was not large enough to handle this extra flow. The first suggestion by the designer was to increase the size of the control valve, an obvious solution you might think. The first problem was that it would need larger diameter hoses (difficult to get onto the valve) but more importantly the valve looses its sensitivity due to the flow gain of the larger valve. Being a proportional valve and using a joystick with electrical control the winch would not have the sensitivity and less easy to control at low speed.
The better option is to fit and unloading valve directly off the pump outlet. When unloaded half the flow could pass through the unloading valve and half through the control valve. When the engine speed is reduced to 1000rpm the unloading valve can be closed allowing the reduced flow to pass to the control valve and operate the winch at the correct speed.
When driving pumps using engines especially with fixed displacement pumps you should always consider the working and the maximum rpm of the pump. It might be necessary to adjust the specification to cater for the extra flow.
Attributed to: Omar Khayam, 13th century philosopher
He who knows not, and knows not that he knows not, is a fool. Shun him.
He who knows not, and knows that he knows not, is a child. Teach him.
He who knows, and knows not that he knows, is asleep. Wake him.
He who knows, and knows that he knows, is a leader. Follow him.
Very best
Bob Jackson (The Hydraulic man)
More hydraulics at www.hydraulicbrain.com
Saturday 31 March 2012
Tuesday 20 March 2012
What is the difference between airation and cavitation?
Often miss diagnosed and not surprising because the symptoms are similar but with very different causes.
Airation
Very simply this is the result of air getting into the hydraulic fluid and most likely through the suction pipe or if the oil level has been allowed to get too low, partially uncovering the inlet to the pump. The pump will sound noisy (lumpy), a very similar noise to cavitation and undesirable for the following reasons.
1) The system becomes spongy and movements become erratic with pressure fluctuations.
2) The lubrication of the sliding parts within the pump etc will be reduced and lead to failure.
3) Dieseling effect could cause ignition with very high temperature spots, damaging seals
The Cure: The suction pipe will be subject to vacuum so do not expect to see any oil leak so best check all fittings between the strainer and pump inlet. Another way is a little messy but try grease or oil around the joints and listen for pump tone change.
Cavitation There are many reasons for cavitation but they all result in restricting oil entering the pump.
Best to start with easy stuff first:
1) Tank breather blocked (remove and replace)
2) Suction valve not fully open
3) Oil cold or too thick (check viscosity)
4) Suction Strainer clogged (remove and replace)
5) Suction pipe too small
6) Suction pipe too long
7) Pump speed too high
Cavitation is very destructive and will damage the pump in a very short time. Minute explosions take place on the surface of the metal during the transition from vacuum to high pressure with temperatures reaching greater than that on the sun. Pitting and metal removal will quickly lead to failure.
Hope you find this interesting and helpful and you can find more valuable information if you sign up at www.hydraulicbrain.com
Keep safe
Bob Jackson (The Hydraulic man)
Airation
Very simply this is the result of air getting into the hydraulic fluid and most likely through the suction pipe or if the oil level has been allowed to get too low, partially uncovering the inlet to the pump. The pump will sound noisy (lumpy), a very similar noise to cavitation and undesirable for the following reasons.
1) The system becomes spongy and movements become erratic with pressure fluctuations.
2) The lubrication of the sliding parts within the pump etc will be reduced and lead to failure.
3) Dieseling effect could cause ignition with very high temperature spots, damaging seals
The Cure: The suction pipe will be subject to vacuum so do not expect to see any oil leak so best check all fittings between the strainer and pump inlet. Another way is a little messy but try grease or oil around the joints and listen for pump tone change.
Cavitation There are many reasons for cavitation but they all result in restricting oil entering the pump.
Best to start with easy stuff first:
1) Tank breather blocked (remove and replace)
2) Suction valve not fully open
3) Oil cold or too thick (check viscosity)
4) Suction Strainer clogged (remove and replace)
5) Suction pipe too small
6) Suction pipe too long
7) Pump speed too high
Cavitation is very destructive and will damage the pump in a very short time. Minute explosions take place on the surface of the metal during the transition from vacuum to high pressure with temperatures reaching greater than that on the sun. Pitting and metal removal will quickly lead to failure.
Hope you find this interesting and helpful and you can find more valuable information if you sign up at www.hydraulicbrain.com
Keep safe
Bob Jackson (The Hydraulic man)
Thursday 15 March 2012
What is pressure compensation?
So what is pressure compensation?
For any flow of fluid through a pipe there must be a pressure drop with greater pressure at the source of flow (pump) and lessoning the further you go downstream. This is due to the frictional losses in pipe, fittings, valves, filters etc and we call this Pressure Drop or Delta P and often signified using the symbol (ΔP). If there is no difference in pressure then there will be no flow.
If the pressure difference (ΔP) is constant then the flow and hence the speed of the actuator will also be constant but if the flow or load changes there will also be a change in the pressure drop and consequently change in speed of the actuator.
With some applications, constant speed of a ram or motor can be very important, take an application like a hydraulic passenger lift. It is important that the speed with only one passenger is the same as when the lift is full of people. Without compensating for the pressure difference the speed would change. With more people in the lift the downward speed would increase and with just one person might be unacceptably slow.
So we need a valve that will automatically close down and reduce flow when the load is greater and open when the load is less or a pump that will increase flow or decrease flow to maintain a constant Delta P.
With a speed control valve make sure it is a pressure compensated type and sized correctly for the flow. To maintain Delta P with the pump use a load sensing option. Variable piston and vane pumps only have this option available. A load sensing pump will automatically adjust the flow to the required load and maintain the correct speed. Another benefit with this type of arrangement is power saving and less heat generation.
Bob Jackson (The Hydraulic man)
More interesting stuff at www.hydraulicbrain.com
For any flow of fluid through a pipe there must be a pressure drop with greater pressure at the source of flow (pump) and lessoning the further you go downstream. This is due to the frictional losses in pipe, fittings, valves, filters etc and we call this Pressure Drop or Delta P and often signified using the symbol (ΔP). If there is no difference in pressure then there will be no flow.
If the pressure difference (ΔP) is constant then the flow and hence the speed of the actuator will also be constant but if the flow or load changes there will also be a change in the pressure drop and consequently change in speed of the actuator.
With some applications, constant speed of a ram or motor can be very important, take an application like a hydraulic passenger lift. It is important that the speed with only one passenger is the same as when the lift is full of people. Without compensating for the pressure difference the speed would change. With more people in the lift the downward speed would increase and with just one person might be unacceptably slow.
So we need a valve that will automatically close down and reduce flow when the load is greater and open when the load is less or a pump that will increase flow or decrease flow to maintain a constant Delta P.
With a speed control valve make sure it is a pressure compensated type and sized correctly for the flow. To maintain Delta P with the pump use a load sensing option. Variable piston and vane pumps only have this option available. A load sensing pump will automatically adjust the flow to the required load and maintain the correct speed. Another benefit with this type of arrangement is power saving and less heat generation.
Bob Jackson (The Hydraulic man)
More interesting stuff at www.hydraulicbrain.com
Saturday 3 March 2012
Eco Friendly Hydraulic Oil
The oil that flows through hydraulic systems can almost be compared with blood which flows through our bodies and like blood; any problems with the oil can affect components, performance or serious failure of the hydraulic system. Hydraulic oils can vary in their formulations using different additives to improve the system performance and protect components against wear and corrosion. In recent years new synthetic oils have become available and the ones most interesting to me are those that cause less damage to the environment if accidentally spilt on land, sea or rivers.
When we designed the recent hydraulic system for the open 60 racing Yacht “Acciona” our client stressed that the hydraulic system should present no risk of contamination to the sea. The amount of oil carried on this type of boat is very small compared to industrial applications but even one litre of mineral oil accidentally spilt into the sea is still far too much and not acceptable if we are serious about keeping our oceans free of pollution.
Rape seed oil has been available for many years for environmentally sensitive applications but do not offer the same protection to hydraulic components as mineral oils but synthetic based oils are a new generation of “Eco” oils that offer greater benefits for systems and environment.
We contacted Millers Oils who recommended Millmax 32HFD(u).
I wanted to know (in laymen terms) how effective the oil was in protecting the environment and hydraulic components and this is their reply:
Definitely would not recommend you drink it, would have a similar effect to drinking Castor Oil.
Would not kill fish as any escaped oil would lie on the surface oil while it was biodegrading away (being eaten by bacteria)
Synthetic esters which is made from are reaction products of fatty acids and alcohols, careful selection of the two components can radically change the end product.
They will provide better protection than mineral oils and also give better lubricity (more slippery) providing the oil stays at sensible temperature i.e. kept below 80˚C they will outlast a mineral oil
For us it is still early days to properly evaluate this oil but so far it has performed well. At the moment these oils can be five times the price of mineral oil but if it is as good as the manufacturer’s claim then I believe that we should be consider it for more applications especially where there is any risk to the environment.
Bob Jackson (The Hydraulicman)
For more hydraulics see www.hydraulicbrain.com
When we designed the recent hydraulic system for the open 60 racing Yacht “Acciona” our client stressed that the hydraulic system should present no risk of contamination to the sea. The amount of oil carried on this type of boat is very small compared to industrial applications but even one litre of mineral oil accidentally spilt into the sea is still far too much and not acceptable if we are serious about keeping our oceans free of pollution.
Rape seed oil has been available for many years for environmentally sensitive applications but do not offer the same protection to hydraulic components as mineral oils but synthetic based oils are a new generation of “Eco” oils that offer greater benefits for systems and environment.
We contacted Millers Oils who recommended Millmax 32HFD(u).
I wanted to know (in laymen terms) how effective the oil was in protecting the environment and hydraulic components and this is their reply:
Definitely would not recommend you drink it, would have a similar effect to drinking Castor Oil.
Would not kill fish as any escaped oil would lie on the surface oil while it was biodegrading away (being eaten by bacteria)
Synthetic esters which is made from are reaction products of fatty acids and alcohols, careful selection of the two components can radically change the end product.
They will provide better protection than mineral oils and also give better lubricity (more slippery) providing the oil stays at sensible temperature i.e. kept below 80˚C they will outlast a mineral oil
For us it is still early days to properly evaluate this oil but so far it has performed well. At the moment these oils can be five times the price of mineral oil but if it is as good as the manufacturer’s claim then I believe that we should be consider it for more applications especially where there is any risk to the environment.
Bob Jackson (The Hydraulicman)
For more hydraulics see www.hydraulicbrain.com
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