If the minimum pressure pulsation points coincide with the expansion phase as the side flow areas open up, it might result in some malfunctions or poor performance. In a gear pump, the friction torque and consequent pump operation and required power can be affected by liquid temperature as well as operating pressure and pump speed.
When the pressure differential is large, the friction torque decreases first and then increases with an increase in pump speed. For a large pressure differential, the friction torque could become higher with an increase in liquid temperature in a low pump speed region, but it could have the opposite tendency in a high pump speed region. When a gear pump operates with a relatively low suction pressure for instance, when liquid is from a tank at a lower level , pressures in the suction piping and chamber get closer to vapor pressure, and cavitation can take place upstream from the gear meshing region.
Another common operational problem is cavitation in the case of transient operations. One frequent cause of cavitation is insufficient flow into the expanding inter-tooth volumes. In many theoretical or operational studies on these topics, the inter-tooth volumes that are formed at the roots of the driver and driven gears should be considered.
Compressible flow into and out of these volumes plays important roles in cavitation and transient operation. To study the effects of operation parameters such as suction pressure on pump operation, in a case study a gear pump has been operated at 1, rpm and 3, rpm speeds with around 20 Barg discharge pressure.
The pump suction is from an atmospheric tank. In other words, at around 3, rpm, the gear pump should be operated with a mean suction absolute pressure of 0. At 1, rpm, this same situation represented a smaller suction pressure drop of only about 0. Gear pumps can usually come in single or double two sets of gears pump configurations with different types of gear such as spur, helical, herringbone gears.
Helical and herringbone gears typically offer a smoother flow compared to spur gears, although all gear types are relatively smooth. Straight spur gears are easiest to cut and are the most widely used. Helical and herringbone gears run more quietly but cost more. They are typically used in large capacity gear pumps. Displacement volumes of a gear pump are directly affected by the gear tooth profile.
Since the involute gear tooth profile is easily manufactured and the technology for the power transmission gear can be applied, this profile is usually adopted for a low cost gear pump. In an involute gear, the profiles of the teeth are involutes of a circle. The pressure angle is the acute angle between the line of action and a normal to the line connecting the gear centers. Theoretically, gear manufacturers can produce any pressure angle.
However, the most common gears have a 20 degree pressure angle, with Increasing the pressure angle increases the width of the base of the gear tooth, leading to greater strength and load carrying capacity. Decreasing the pressure angle provides lower backlash, smoother operation and less sensitivity to manufacturing errors. Many gear pumps use helical gears. The teeth on helical gears are cut at an angle to the face of the gear.
When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement. This gradual engagement makes helical gears operate more smoothly and quietly than spur gears. Because of the angle of the teeth on helical gears, a thrust load axial load is created on the gear when they mesh.
This load should be properly addressed, for example, by using thrust axial bearings. The use of helical gears is indicated when the application involves relatively high speeds, relatively high power pumps or where noise abatement is important.
As an indication, the speed might be considered to be high when the pitch line velocity exceeds 20 meters per second. A herringbone gear is a specific type of double helical gear that is a side-to-side combination of two helical gears of opposite hands.
Like helical gears, herringbone gears have the advantage of operating smoothly because more than two teeth will be in mesh at any moment in time. Their advantage over the helical gears is that the side-thrust of one half is balanced by that of the other half. The pump is always trying to put out a particular pressure. The more you resist that it will just reduce flow.
There are advantages to this such as controlling flow, but also maintaining [inaudible ] flow control or through a valve. Rather than just always giving you full flow and full pressure, this will just give you the pressure you want and cut back flow to compensate for a higher pressure. The advantages and disadvantages of a vane pump is they are quiet.
Especially ones where there are humans around to be annoyed or not annoyed by a pump, these are a good choice. They are relatively contamination resistant. Luckily they can be easily repaired, so should contamination become a problem in them, they can be fixed quite easily. They are relatively inexpensive, especially the fixed vane pump.
As you go through the costing of a pump, you have your cheap gear pumps and you can have an inexpensive fixed vane pump which would kind of come in at the high end of a gear pump and then go up in price from there. One of the reasons is that as you spin a vane pump fast the vanes, because of centrifugal force, kind of get pushed out too deep into the cam ring. They can wear more quickly. Anyway, vane pumps can also get very expensive. Some of the top brands they have some pretty fancy designs.
They can be really complex to set up and run, but still, like I said, not as expensive as most piston pumps. Also one of the disadvantages that they have low pressure capacity. Not more than two or 3, psi. Piston pumps is a familiar closed-loop type pump.
Three types of piston pumps. All three of these are nice designs and fairly common, each to the piston pump family. These can be had in fixed displacements, just like in a gear pump or a vane pump. This particular one is a pressure compensated load-sensing pump. What we have here is we have instead of a bias piston, this one actually has a bias spring. What the spring here is doing, it has a lot of force. The volume would be reduced. If this was a severe angle, so if it was angled across this way, you can imagine that the pistons would travel a far distance.
They would go in and out very far, so it would increase and decrease displacement at a higher volume. The bias piston tries to do its best to always have full displacement and how displacement decreases is with the control piston right here. Similar to the one that was in the vane pumps.
This one here is controlled by the relief valve in the compensator up here. Whatever pressure you have this set to is the pressure that this thing wants to push backwards on the swash plate to try to get it to go to a zero angle. As pressure increases, so if you were to increase or decrease the pressure on this compensator here, it increases or decreases the force which this control piston pushes on the swash plate.
If you raise the pressure on this compensator to resist this pump and then subsequently have it go on standby. We have the bent axis piston pump. You can see that the input shaft comes in a one five and the rotating group and the ports will be on an angle to the input shaft.
If you were to have this pulley-driven, so if you imagine that the forces on a pulley were being driven from below, the angle that is on the bent axis really resists those side note forces that are put onto a shaft. If you were to have a pump that required for some reason because of space or design to be run by say a chain or a pulley, a bent axis piston pump is the way to go. These things can rotate very quickly and they can also withstand very high pressures.
Hydraulic pumps, this is the radial piston pump. I always compare it to an airplane engine. The dump pump is unsuited for continuous-duty applications because of its narrow, internal paths and the subsequent likelihood of excessive heat generation.
With a dump pump, either a two- or three-line installation must be selected two-line and three-line refer to the number of hoses used to plumb the pump ; however, a dump pump can easily be converted from a two- to three-line installation. Many dump bodies can function adequately with a two-line installation if not left operating too long in neutral. When left operating in neutral for too long however, the most common dump pump failure occurs due to high temperatures.
To prevent this failure, a three-line installation can be selected — which also provides additional benefits. Pumps for refuse equipment include both dry valve and Live Pak pumps. Both conserve fuel while in the OFF mode, but have the ability to provide full flow when work is required. While both have designs based on that of standard gear pumps, the dry valve and Like Pak pumps incorporate additional, special valving. Primarily used on refuse equipment, dry valve pumps are large displacement, front crankshaft-driven pumps.
The dry valve pump encompasses a plunger-type valve in the pump inlet port. As a result, the horsepower draw is lowered, which saves fuel when the hydraulic system is not in use. In the closed position, the dry valve allows just enough oil to pass through to maintain lubrication of the pump. This oil is then returned to the reservoir through a bleed valve and small return line.
A bleed valve that is fully functioning is critical to the life of this type of pump, as pump failure induced by cavitation will result if the bleed valve becomes clogged by contaminates. Muncie Power Products also offer a butterfly-style dry valve, which eliminates the bleed valve requirement and allows for improved system efficiency. Trying to fit a standard gear pump to a dry valve likely will result in premature pump failure.
Live Pak pumps are also primarily used on refuse equipment and are engine crankshaft driven; however, the inlet on a Live Pak pump is not outfitted with a shut-off valve. With a Live Pak pump, the outlet incorporates a flow limiting valve. This is called a Live Pak valve. As a result, the hydraulic system speed is limited to keep within safe operating parameters.
Types of Hydraulic Pumps. June 29, Whitney VanKlaveren. Gear Pumps For truck-mounted hydraulic systems, the most common design in use is the gear pump. Quick Look Most common design Fewer moving parts, easy to service, more tolerant of contaminates, relatively inexpensive Fixed, also called positive, displacement pumps Rated in terms of max pressure rating, cubic inch displacement, max input speed limitation Used in open center hydraulic systems Transports oil around circumference of gear cavity and forces it through outlet port Encompasses thrust plates that push against gear ends with small amount of pressurized oil to improve pump efficiency Piston Pumps When high operating pressures are required, piston pumps are often used.
0コメント