Gear pump standard?

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hobgobbln
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Gear pump standard?

Post by hobgobbln »

Is there something like NEMA sizes for hydraulic gear pumps? Or is there a small cheap gear pump that is used like everywhere?

I am unfamiliar with hydraulics and need to do some experimentation. Looking around for pumps I don’t seem to find anything that says a mounting type or standard.

Griz
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Steggy
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Re: Gear pump standard?

Post by Steggy »

hobgobbln wrote: Fri Jun 03, 2022 7:19 amIs there something like NEMA sizes for hydraulic gear pumps? Or is there a small cheap gear pump that is used like everywhere?

I am unfamiliar with hydraulics and need to do some experimentation. Looking around for pumps I don’t seem to find anything that says a mounting type or standard.

Face-mounted hydraulic pumps are usually described in SAE types, e.g., A, B, etc. For example, the pump in my F-unit has an SAE type B face with two mounting holes—there is also a four-hole version. The SAE type describes the mounting bolt pattern, bolt hole diameter—1/2" for SAE type B, and the diameter of the register used to center the pump on whatever supports it. The SAE type doesn’t describe the input shaft itself, which may be splined, keyed, etc.
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Bill Shields
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Re: Gear pump standard?

Post by Bill Shields »

Gear pumps, like every pump, are sized by mechanical connections AND pressure / flow at a given rpm and available HP.

There is no one size fits all.

The pump you would use on a log splitter and one that would drive a bush hog...may have the same bolt pattern and shaft size ...but may very well be quite different in terms of hydraulic specifications.
Too many things going on to bother listing them.
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Re: Gear pump standard?

Post by Steggy »

Bill Shields wrote: Fri Jun 03, 2022 9:36 pmGear pumps, like every pump, are sized by mechanical connections AND pressure / flow at a given rpm and available HP.

The foremost characteristic of a hydraulic pump is its displacement, which is measured in cubic inches per revolution in the USA—virtually all pump characteristics are based on its displacement.

Flow rate is determined by the pump’s displacement, the speed at which it is run and its efficiency. Theoretical flow is independent of pressure. Developed pressure is proportional to input power and resistance to flow. The flow/pressure relationship implicitly determines power-transmission capacity.

No hydrostatic system operates at 100 percent efficiency, the two factors controlling overall efficiency being blowby and volumetric efficiency. The former is a function of the pump's design and condition—new, broken-in or worn. Most vane pumps exhibit lower blowby than gear pumps, but gear pumps are longer-lasting and are able to tolerate higher pressures. Although a negligible factor in most systems, blowby also occurs in some types of valves, spool valves being typical. On the other hand, volumetric efficiency is mostly a function of the design and implementation of the piping and control package.

Applied pressure at the motor determines the amount of torque generated. This is a function of loading and tends to be self-controlling in most systems. The worst-case scenario is one in which the load is immobilized, such as a cylinder being driven to full travel and then continually pressurized. This condition is referred to as hydrostatic lock. With hydrostatic lock, pressure theoretically becomes infinite. In practice, the pump’s prime mover will stall or a mechanical failure will occur.

Hydrostatic lock isn’t going to arise with a large-scale locomotive, since wheelslip will occur or the prime mover will quit due to being overloaded. Therefore, extremely high pressures will not occur. Peak pressures are developed at startup and quickly diminish as the locomotive accelerates. In my F-unit, I designed for a continuous pressure of 1800 PSI, which is about a 20 percent safety margin above the maximum calculated 1450 PSI that would be generated at full throttle with the train stalled.

In designing a hydrostatic power transmission, the three factors to be considered are the desired speed ratio between prime mover and load, desired torque at the load and the maximum speed at which the load is to be driven. Knowing the desired load torque and speed makes it possible to compute the horsepower required to drive the load. Knowing the load speed makes it possible to compute the ratio between pump displacement and motor displacement—the displacement ratio is the hydrostatic equivalent of the tooth ratio between gears.

With these factors known, the process becomes one of selecting a pump with the required input horsepower capacity and a motor with the correct displacement to achieve the desired speed ratio with the selected pump. Actual input horsepower required to produce the desired load horsepower will be higher than calculated due to pump blowby and piping and control package losses.

Speaking of efficiency, it helps to understand it so a better-performing system can be build.

Pump blowby tends to increase with discharge pressure and pump temperature, but lessens in proportion to displacement as pump speed increases. A pump whose housing and covers are iron or cast steel will exhibit less blowby under all conditions than a pump with aluminum housings, with the difference widening as pressure and/or temperature increases. Higher blowby means less efficiency, since some input power is being used to force oil past pump elements, resulting in heat. In the case of aluminum pumps, the extra heat generated by blowby can cause pump temperature to rise to a point at which more blowby will occur, causing a spiraling loss of efficiency. Also, that heat can result in seal failure. For these reasons, I strongly recommend that aluminum pumps be avoided. The iron ones cost more money, but are much more robust and efficient under load.

Volumetric efficiency tends to be where the largest losses occur and mostly are found in the piping. For example, using threaded pipe, as seen in the OP’s photo, causes losses due to turbulence, primarily a result of discontinuities between pipe sections and fittings. This characteristic is exacerbated by the tight radii in commercial pipe fittings.

Another source of volumetric efficiency loss is forcing the pump to draw oil “up hill” from the reservoir, which can result in the pump inlet operating at a negative pressure. If the oil temperature is sufficiently high, the result will be pump inlet cavitation, which will cause pump efficiency to nosedive. In some cases, cavitation can result in pump damage. This sort of thing is avoidable by arranging for the pump's inlet to be below the level of the oil in the reservoir—the lower the better.

Still another volumetric efficiency thief, and an insidious one at that, is excessive use of hose in the overall piping setup. Hoses are inherently restrictive due to discontinuities between the hose itself and the fittings. Hoses, of course, can’t be avoided, since they are de rigueur at the trucks. Also, it is wise to connect the oil reservoir to the rest of the system with hose. Here, the hose should be relatively large in diameter to minimize its effect on volumetric efficiency.

That said, the rest of the system should be piped with pressure-rated steel tubing mated to appropriately-sized JIC fittings. Avoid pipe fittings as much as you can. If a part, such as a control valve, is available with SAE O-ring ports as well as NPT ports, take the former. Select tubing sizes with the understanding that flow through a piece of tubing of a given length at a given pressure is proportional to the square of the inside diameter. I used 1/2" diameter DOM tubing with 0.049" walls to maximize flow under pressure. It should also be understood that one 90 degree elbow in the system produces as much restriction as a 10 foot length of straight tubing of a matching diameter.

A not-so-obvious gain from piping with pressure-rated tubing is a cooler-running system. Hose has poor heat rejection, which usually means an oil cooler has to be part of the system to keep a lid on temperatures. My F-unit doesn’t have or need an oil cooler—the piping acts as the radiator. Plus the system has less restriction than one piped with hose, which automatically reduces the amount of waste heat produced. That translates to more horsepower to run the train.
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hobgobbln
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Re: Gear pump standard?

Post by hobgobbln »

BigDumbDinosaur wrote: Fri Jun 03, 2022 1:31 pm The SAE type describes the mounting bolt pattern, bolt hole diameter—1/2" for SAE type B, and the diameter of the register used to center the pump on whatever supports it. The SAE type doesn’t describe the input shaft itself, which may be splined, keyed, etc.
That’s good to know. I didn’t notice SAE being mentioned while I was looking around but I’ll look more closely now.
Bill Shields wrote: Fri Jun 03, 2022 9:36 pm The pump you would use on a log splitter and one that would drive a bush hog...may have the same bolt pattern and shaft size ...but may very well be quite different in terms of hydraulic specifications.
For what I’m doing it probably won’t matter, but I’ll keep that in mind as well.

Since the SAE mount doesn’t include the shaft in the specs, is there a super common cast iron gear pump? This project will be going out of state and I am just starting the design so I’d like to find a pump that’s readily available in case something goes wrong 6 months later. I always try to make things so somebody can fix it later instead of tossing it.

Griz
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Steggy
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Re: Gear pump standard?

Post by Steggy »

hobgobbln wrote: Sat Jun 04, 2022 12:44 pmSince the SAE mount doesn’t include the shaft in the specs, is there a super common cast iron gear pump? This project will be going out of state and I am just starting the design so I’d like to find a pump that’s readily available in case something goes wrong 6 months later. I always try to make things so somebody can fix it later instead of tossing it.

You haven’t indicated the prime mover capabilities, i.e., horsepower at a given RPM, so it’s kind of difficult to make a recommendation. However, a possible choice would be a Haldex-Concentric F15-series pump or the older Haldex G25 pump, which is what I use in my F-unit. I know the F15 is current production and, in fact, is in widespread use. I’m not sure of the G25's production status. The G25 is meant for higher horsepower applications and is more robustly constructed. Both series have iron housings and end plates. I can vouch for the G25's performance—it’s an excellent pump.

I’ve attached the G25 catalog for your reading pleasure. I tried to attach the F15 catalog but the forum software won't let me, possibly due to size. It would be nice if the software offered some useful diagnostics when it refuses to accept an upload.

g25catalog.pdf
Barnes-Haldex G25 Gear Pump
(251.13 KiB) Downloaded 162 times
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hobgobbln
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Re: Gear pump standard?

Post by hobgobbln »

BigDumbDinosaur wrote: Sat Jun 04, 2022 2:12 pm You haven’t indicated the prime mover capabilities, i.e., horsepower at a given RPM, so it’s kind of difficult to make a recommendation.
That’s because unfortunately I don’t know that info yet.

I need to make a prop that’s spinning by river water and make something else spin about 14’ away. The problem is, it will all be mounted on something that can spin like a turn table so it all needs to be self contained ie, I can’t use electric. Shafting and gears are also out. My plan was to put two gear pumps or a gear pump and small hydraulic motor in a closed loop. The driven pump/motor won’t be required to do any work, it just needs to turn when the pump does. It doesn’t have to turn at the same speed either as long as there’s motion.

I looked into different types of pumps but a small displacement hydraulic gear pump seems to be the best option. The driving pump will most likely be turning at much less than it’s rated speed, but I may be able to fix that with belts and pulleys later. I need to pick up a pump first to experiment with before I’ll know for sure though. That’s why I was looking for a small common pump.

Griz
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Bill Shields
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Re: Gear pump standard?

Post by Bill Shields »

So this js going to be totally submerged and need to be able to rotate about an axis perpendicular to the gear shaft?...or is the gear motor going to be on the turntable axis and out of the water?

You have not indicated the power requirement.

Keep in mind that hydraulic gear pumps are far from being the most efficient way of transferring power..
Too many things going on to bother listing them.
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Re: Gear pump standard?

Post by hobgobbln »

(Forgive the picture. I couldn’t draw a stick figure even at gunpoint.)

The part that looks like a table will be attached to a floating platform. Basically, I need to transfer motion from A to B. I am going to try and keep the pump out of the water. Think of how a small boat motor works but reverse it so the prop spins the theoretical engine.

From the pump, I need to run lines up INSIDE the vertical shaft to a motor somewhere in the mystery cloud above the turn table. The mystery cloud, turntable, vertical shaft and prop all need to be able to turn as one, but independently from the platform which is why it must be self contained.

I have no idea what the power requirements will be. I don’t even know what axis the motor will be in inside the mystery cloud. Someone else is building that. This is all still in the drawings on a napkin phase which is why I need to do some experiments. I need to pick up a small gear pump and motor to start with and see how it reacts at super low speeds first and build the rest of it around that. Like I said, I’m not concerned with generating much force. I just need to transfer the rotary motion.

Griz
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Bill Shields
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Re: Gear pump standard?

Post by Bill Shields »

I would drive a dc generator rather than a gear motor pump. Properly designed the housing of the generator will be stationary.

At SLOW rpm the gear pumps is a pig and supporting a hydraulic system is a PITA
Too many things going on to bother listing them.
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NP317
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Re: Gear pump standard?

Post by NP317 »

Sounds like an outboard motor lower unit might work!
Food for thought.
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Re: Gear pump standard?

Post by Steggy »

Bill Shields wrote: Sat Jun 04, 2022 3:32 pmKeep in mind that hydraulic gear pumps are far from being the most efficient way of transferring power.

As pumps go, spur gear designs are pretty efficient. However, overall efficiency of hydrostatic power transmission rarely exceeds 60 percent.

Now that we know something about the application, I have to ask why mechanical power transmission can’t be used.
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