mikehaugen
Elite Member
I agree that a variable displacement pump would be worth trying to find. I think it would save you a ton of fuel.
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40gpm log s[litter valve
- Thread starter muddstopper
- Start date
- Views: 4999
CJONE
Veteran Member
I agree that a variable displacement pump would be worth trying to find. I think it would save you a ton of fuel.
?? With multiple circuits working at the same time at different pressures/flows it is extremely hard if not impossible to keep everything correct with a 1 circuit v/d pump. Remember when you are not using a function with open circuit hydraulics it is just flow returning back to tank, very little fuel use or load. CJ
mikehaugen
Elite Member
If you are talking open center then I agree about the fuel usage, but it would be more difficult to keep everything right with oc, unless everything comes out of a single valve bank. A vd pump would be easy, it will displace as much as it needs to in order to maintain a preset pressure. Just about every power unit at my work uses a vd pump with as many as 20 (maybe more) circuits coming off of it.
mikehaugen
Elite Member
If a certain circuit needs less pressure than that preset you can put a regulator in that circuit.
mikehaugen
Elite Member
Most gear pumps that I see are cc, with one relief valve to regulate pressure, so the pump is constantly running full displacement and pressure... very inefficient.
mikehaugen
Elite Member
Btw, I am referring to axial piston pumps... not too familiar with other types of vd pumps.
CJONE
Veteran Member
Gear pumps are used in o/c systems, very rarely are they used with cc systems and when they are they include a dump valve to unload a checked circuit like a accumulator. Gear pumps do not dump over a pressure control, if they did they will quickly overheat a system.[I deal with this mistake ALOT] A gear pump gives you the pressure to do the job, no more until it hits the relief. 1 large VD pressure comp pump would need pressure compensating flow controls in each circuit to keep rpm and speed in control, a simple flow control would not do be cause of load variations and temp. The cost of this is very prohibitive verses a multi circuit gear pump that will always give you the same flow per circuit no matter the pressure differences. You must work in a factory or industrial setting. I could put 100 valves into a closed center system but if 1 valve required the full flow of the pump at a lower pressure than any of the other valves that is working, only that circuit will function. I do this every day. Yesterday was fixing a press that a customer spent thousands on throwing parts at it for a year and it was fixed in 20 minutes with a simple flow control. Anyway fun fun. CJ
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mikehaugen
Elite Member
1 large VD pressure comp pump would need pressure compensating flow controls in each circuit to keep rpm and speed in control, a simple flow control would not do be cause of load variations and temp.
I don't understand this part of your response. I do work in a factory, and am used to electric motors powering hydraulic pumps... they don't change speed, maybe that's the difference?
90% of the pumps we have are axial piston vd pc pumps. They have a swash plate the will change angle so when there is no demand and it reaches some predetermined pressure (set on pump) the displacement drops to near zero. As soon as there is flow (demand) the swash plate angles and allows the pistons to displace fluid to keep the pressure steady, regardless of flow. It doesn't matter if there is one valve open or 20, as long as the the demand does not exceed the maximum displacement of the pump.... the pressure does not change.
I think you probably know this, but just pointed it out so you know my thinking. Maybe there is a difference between the industrial applications that I am used to and whatever you are used to. Not trying to argue, maybe there is an opportunity for me to learn something too. I don't know how one of these pumps would behave behind an engine that is probably not tightly governed, as I said an electric motor is more or less constant.
Anyway, sorry to derail the thread, the op was asking about valves. You can pm me to discuss this more if you like, I am always up for constructive discussion and/or learning.
CJONE
Veteran Member
I don't understand this part of your response. I do work in a factory, and am used to electric motors powering hydraulic pumps... they don't change speed, maybe that's the difference?
90% of the pumps we have are axial piston vd pc pumps. They have a swash plate the will change angle so when there is no demand and it reaches some predetermined pressure (set on pump) the displacement drops to near zero. As soon as there is flow (demand) the swash plate angles and allows the pistons to displace fluid to keep the pressure steady, regardless of flow. It doesn't matter if there is one valve open or 20, as long as the the demand does not exceed the maximum displacement of the pump.... the pressure does not change.
I think you probably know this, but just pointed it out so you know my thinking. Maybe there is a difference between the industrial applications that I am used to and whatever you are used to. Not trying to argue, maybe there is an opportunity for me to learn something too. I don't know how one of these pumps would behave behind an engine that is probably not tightly governed, as I said an electric motor is more or less constant.
Anyway, sorry to derail the thread, the op was asking about valves. You can pm me to discuss this more if you like, I am always up for constructive discussion and/or learning.
Real simple. If you have 6 valves and actuate all 6 to run 6 different things and you have 20gpm pump and 1 circuit takes 15gpm at 1000psi and the others take 1 GPM at 2000psi. The circuit that requires 15gpm will now see all the oil 20GPM] overspeeding whatever you are running and the ones that need 2000psi to run will see nothing. The pressure comp pump just provides oil to a pressure setting and the valves just open or close. Flow controls cannot control different flows AND pressure unless they are pressure compensating, $$$$. + you have the added bonus of constantly messing with them. Been there, just not worth it IMHO. CJ
Forgot to add, the prime mover RPM only effects GPM not the distribution of oil.
OP
muddstopper
Veteran Member
I think for my application a stacked pump or a pair of pumps is the best answer. A stacked pump would mean only one mount and be a lot easier to connect to a engine. With a processor, you arent really taking full hp when operating. The saw takes full power when sawing, but you most likely will be advancing the log for another cut while the splitter is cycling. The splitter takes full power to split, but on retract, power requirement is minimal. Even while splitting, the saw probably wont be running before the splitter starts it return stroke. Ideally, the splitter would just be starting its retract about the time the saw starts cutting the round and the saw should drop the cut just as the splitter is fully retracted. Everything would have to be perfect and uniform to make that happen. I have timed large saws in large rounds and 12sec cuts are not unusual, but in small rounds the cut might just take 5 sec. It would be extremely hard to work fast enough that every function of a processor would need to operate at the same time. I am just hoping that I can cut and split a round every 12-15sec and with a hydraulic chainsaw, that might be asking to much. It easy to get 12 sec cycle times with a splitter, but every log aint the same when it comes to sawing into blocks.
