When I first started out designing systems we had the choice between vane or piston pumps.
Gear pumps at that time were rather frowned upon and not readily available.
I haven’t used a fixed vane pump since I can remember and piston pumps only for occasions when I need high pressure or my customer is keen on quality/reliability rather than cost.
There is no doubt that the gear pump has become more popular but maybe our hydraulic group may not all agree with this trend.
Personally I will use a variable vane for those systems where I need to hold pressure for long periods with low pressure. The piston pump for higher pressure, long periods on pressure with big flows. The gear pumps for everyday low duty and competitively priced.
You will all have your own ideas for selecting the ideal pump and I would love to hear your views.
Very best
Bob
Wednesday 18 May 2011
Saturday 7 May 2011
Tuesday 3 May 2011
Hydraulic Oil
We talk a great deal about pumps, valves, pipe-work and other hardware but give little mention about the lifeblood of the system, that of course is hydraulic oil.
This is vitally important to the life and performance of the system and come in many varieties.
When I started my career we were told to say that any oil is ok as long as it is mineral ISO 32 hydraulic oil and I suppose it is still the most common choice today.
But we also have applications where this is not suitable and today we have more choices and better oils to better suit demanding conditions.
The environment has become a greater issue and it is very important we do not contaminate the soil or waterways. Rape seed oils were common but now there are some very good synthetic oils that not only protect the environment but are better suited to the components.
Fire has long been an issue with fire resistant fluid. Water glycols must be used with overhead tanks due to specific gravity and to avoid cavitation. However there are fluids that can be used in the same way as normal oil that give similar protection.
Skydrol is used in aerospace systems and will destroy most types of rubber and plastic and need careful selection of pumps and valves.
It might be that the system is working in very hot or very cold environments and will need a suitable grade of oil that will end up with the ideal viscosity at the working temperature.
There are also oils that will not degrade when run at higher temperatures.
With mineral oils, I do not like temperatures above 50centigrade (comfortable to the touch).
Higher temperatures can cause many problems with seals, varnishing and eventually breakdown of the additives that protect the systems.
I would like to hear about oils that our group has used and maybe stories of problems when unsuitable oil is used.
Cheers
Bob
This is vitally important to the life and performance of the system and come in many varieties.
When I started my career we were told to say that any oil is ok as long as it is mineral ISO 32 hydraulic oil and I suppose it is still the most common choice today.
But we also have applications where this is not suitable and today we have more choices and better oils to better suit demanding conditions.
The environment has become a greater issue and it is very important we do not contaminate the soil or waterways. Rape seed oils were common but now there are some very good synthetic oils that not only protect the environment but are better suited to the components.
Fire has long been an issue with fire resistant fluid. Water glycols must be used with overhead tanks due to specific gravity and to avoid cavitation. However there are fluids that can be used in the same way as normal oil that give similar protection.
Skydrol is used in aerospace systems and will destroy most types of rubber and plastic and need careful selection of pumps and valves.
It might be that the system is working in very hot or very cold environments and will need a suitable grade of oil that will end up with the ideal viscosity at the working temperature.
There are also oils that will not degrade when run at higher temperatures.
With mineral oils, I do not like temperatures above 50centigrade (comfortable to the touch).
Higher temperatures can cause many problems with seals, varnishing and eventually breakdown of the additives that protect the systems.
I would like to hear about oils that our group has used and maybe stories of problems when unsuitable oil is used.
Cheers
Bob
Sunday 1 May 2011
Valve leakage
I hear a lot of myths surrounding leakage.
There have been many times when I have been asked to design a system where the client wants to hold a load almost indefinitely (leak free).
Most sliding valves need some leakage for lubrication due to metal to metal contact. Poppet valves or seated valves are as good as the next particle of contamination that lodges under the seat. Soft seated valves can give better chance of success but are less available.
The all ports blocked CETOP valve can cause problems with creeping rams. P port being close to A&B with T ports on the far side will allow pressure to A&B and send the ram out. The only remedy is either install a new valve or change to a P to T and a PO check.
Also in the attempt to lock off a load (hydraulicaly) can be dangerous. Any oil passing over the piston and with no route to tank will cause pressure intensification that might be well above the maximum allowed.
I have never relied on valves being leak free and always play safe.
Love to hear your views
Bob
There have been many times when I have been asked to design a system where the client wants to hold a load almost indefinitely (leak free).
Most sliding valves need some leakage for lubrication due to metal to metal contact. Poppet valves or seated valves are as good as the next particle of contamination that lodges under the seat. Soft seated valves can give better chance of success but are less available.
The all ports blocked CETOP valve can cause problems with creeping rams. P port being close to A&B with T ports on the far side will allow pressure to A&B and send the ram out. The only remedy is either install a new valve or change to a P to T and a PO check.
Also in the attempt to lock off a load (hydraulicaly) can be dangerous. Any oil passing over the piston and with no route to tank will cause pressure intensification that might be well above the maximum allowed.
I have never relied on valves being leak free and always play safe.
Love to hear your views
Bob
Subscribe to:
Posts (Atom)