I'm wondering if, or how it's possible to limit or control the hydraulic flow of a gear pump running an FEL or Backhoe so that there's not excessive GPM of hydraulic oil flowing constantly creating unnecessary heat when the FEL isn't being used. I'm going to be running 2 variable piston pumps for the Wheel motors and it's looking like 1 gear pump for accessories, and I need to limit the size of the hydraulic reservoir(there will be a cooler/fan), and I can't seem to find much information about restricting unecessary flow. Would a properly placed solenoid diverter valve be effective at accomplishing this task? Thanks in advance!
Flow Control of Gear Pump
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Rich B1
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A gear pump is a pretty simple positive displacement pump that is simply going to produce a fixed flow that varies with speed. In a typical open center system, you are not going to be consuming that much power or creating that much heat when the implements aren稚 being used.
Any restriction will cause heat consume power. Plus, you say you will have a cooler. The gear pump will provide flow to cool and filter the oil while using the hydrostats.
Any restriction will cause heat consume power. Plus, you say you will have a cooler. The gear pump will provide flow to cool and filter the oil while using the hydrostats.
I found this quote on the forum: "Simplified we can say that, in a CP (Constant Pressure) system, power is regulated by a variable flow, and in a CF(Constant Flow) system, power is regulated by a variable pressure.''
So what your saying is that when the implements aren't being used there isn't much heat being generated because a control valve (Spool?) determines whether the system is pressurized in an open center system? When the valve opens the system becomes pressurized, and therefore functions?
Rich B1
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Yes. In an open center implement circuit, the oil flows thru the valve stack and returns to tank. Until a spool is moved, there is no load as such on the gear pump. As the spool is moved into the work position, pressure will rise as the spool movement directs the pump oil to a work port.
Mixed fixed flow/hydrostatic systems have been used for a long time. And your use of a cooler and filter lets you use your gear system to provide a constant flow of oil for cooling and filtration. IMO, that is a good thing in that type of system
Mixed fixed flow/hydrostatic systems have been used for a long time. And your use of a cooler and filter lets you use your gear system to provide a constant flow of oil for cooling and filtration. IMO, that is a good thing in that type of system
Thanks for that information. So as the spool moves into the work position, the pressure rise is variable? The varying of the pressure/spool valve is what increases or decreases the speed of the FEL cylinders opening and closing? For the sake of argument, if a backhoe and FEL are to be utilized off the same Fixed displacement gear pump (not running at the same time), yet one operates at 10 gpm and the other at 15 gpm, how does one reconcile the different needs of each implement? Essentially they will both function, but will respond to the spool valves in different ways?
RalphVa
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We always had recycle control to control the flow of gear pumps in our refineries. You cannot restrict its discharge. You'll bust something or the pump.
Ralph
Ralph
CobyRupert
Super Member
My understanding is that as the (open center) spool valves moves into the work position, it doesn't directly raise pressure, it diverts flow to a cylinder or some other "end user" (pump, etc..) that presents a resistance/blockage. It's that resistance that builds pressure (from a pump turning out a constant flow) until it's great enough to force the blockage to move (i.e. the cylinder strokes). That is, if the spool valve diverted oil to a cut hydraulic hose line dumping on the ground, there'd be relatively little pressure (unless you tried to restrict the flow).
I would say that the pressure rise is a function of how much mechanical resistance is on that cylinder. That is, if the cylinder has no mechanical load on it and (say, making up numbers) 100 psi can make it stroke, the pressure won't build to more than 100 psi. (Until it hits the end of stroke, then pressure will rise dramatically to the point a relief valve (recycle control?) should open elsewhere; otherwise pump engine stalls or something blows up.)
The oil will flow in the path that has the least resistance when given a choice (i.e. it will stroke the cylinder that needs the least pressure to do so.)
I believe the pump's GPM numbers are really going effect how fast the pump can fill the volume of those cylinders, or multiple cylinders at once, and ultimately how fast you can operate the attachments. I don't think it should effect the pressure of the system or "strength" capacity of the cylinders.
You want a 15gpm pump to operate the larger "15 gpm attachment" at "recommended" speeds.
If I'm in error, I hope somebody else chimes in
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Zebrafive
Super Member
It is not the pressure that determines speed, it is the flow. Pressure will increase until the task is complete or it gets to relief valve setting.
Beeenvenue
Gold Member
You need to be extremely careful when attempting to regulate flow from a gear pump. As a positive displacement device, it will develop extremely high pressures - if you deadhead it, far above what any discharge circuit can handle, until the casing or other component ruptures (usually catastrophically). I am not familiar with the hydraulic circuitry for your application, but if pressure is varying it isn稚 from the pump but rather how the fluid is ported.
The most common way to regulate FLOW is by regulating speed (gear pumps are rated at x gpm/revolution). The amount of power drawn is roughly proportional to the square of the delivered pressure but again, it will develop increasing pressure until it either stalls due to lack of input power or it overcomes any restriction even if that means ruptured hoses. Alternately, you can split the flow into a bypass circuit as others have mentioned. Just do not attempt to use a flow limiting orifice, valve, or common flow control device.
The most common way to regulate FLOW is by regulating speed (gear pumps are rated at x gpm/revolution). The amount of power drawn is roughly proportional to the square of the delivered pressure but again, it will develop increasing pressure until it either stalls due to lack of input power or it overcomes any restriction even if that means ruptured hoses. Alternately, you can split the flow into a bypass circuit as others have mentioned. Just do not attempt to use a flow limiting orifice, valve, or common flow control device.