Ch 5: Hydraulic Pumps
Fixed
All gear pumps are fixed or variable displacement pumps?
Easy
Are variable-displacement, pressure-compensated vane pumps easy or hard to maintain?
It decreases
As pressure requirements in a fluid power system increase, what happens to the efficiency of the pump?
1. Piston = most, Vane = intermediate, Gear = least; 2. Piston = most, Vane = clean, Gear = least; 3. Piston = 3000 to 12,000, Vane = 200 to 3000, Gear = 1500 to 3000; 4. Piston = most, Vane = intermediate, Gear = least; 5. Piston = fixed/variable, Vane = fixed/variable, Gear = fixed; 6. Piston = most, Vane = intermediate, Gear = least; 7. Piston = 80 dB, Vane = 70 dB, Gear = 100 dB;
Between Gear, Vane, and Piston Pumps, answer the following questions... 1. Equipment cost; 2. Operating Environment; 3. Pressure Operating Range; 4. Efficiency; 5. Pump Design; 6. Design Complexity; 7. Loudness;
displacement
Changing the size of the cartridge assembly can change the _____________ of the pump.
the drive gear and driven gear
External gear pumps have two equal-sized gears called what?
creates a vacuum at the inlet and then push the fluid to the outlet by using a decreasing volume
For Gear pumps, what do the meshing gear teeth do?
- 180 - a balanced load on the pump bearings and seals
For balanced vane pumps, the two inlets and two outlets are set ____° apart from each other. What did this create?
positive displacement pumps
For radial piston pumps, the 4 operational steps are the same as what type of pump?
The inner rotor has one less gear tooth than the outer rotor
For the gerotor pump, what are the differences between the gear teeth?
- pressure rating - volumetric displacement per rotation - maximum pressure rating - minimum and maximum operating speeds - overall efficiency, noise level - mounting options - maximum input power (horsepower and kilowatts) - torque range - fluid cleanliness requirements
How are fixed-displacement pumps (positive) rated?
Vane pump assemblies are more complicated and require more time to repair than gear pump assemblies
How are vane pump in comparison to gear pump assemblies?
- maximum pressure rating - minimum and maximum operating speeds - overall efficiency - noise level - mounting options - maximum input power (horsepower and kilowatts) - torque range - fluid cleanliness requirements. - maximum volumetric displacement per rotation - minimum and maximum pressure compensated ranges
How are variable displacement pumps rated?
- by rotation from the prime mover that the angled piston is attached to. - by adjusting the angle at which the pistons and the piston block sit
How does the fixed bent-axis piston pumps work? What about variable bent-axis piston pumps?
by centering the cam ring and controlling the distance that the pistons extend and retract
How is the amount of fluid flow adjusted in a variable pressure-compensated radial piston pump?
with a setscrew that adjusts a control spring.
How is the maximum pilot pressure set in a pressure-compensated variable- displacement inline axial piston pump?
by increasing the volume of fluid at their inlet and decreasing the volume of fluid at their outlet
How to hydraulic pumps create flow?
the speed at which they operate or their internal components
Hydraulic fixed-displacement pumps cannot vary the amount of fluid flow that they produce during operation without changing what?
systems that do not require variation in system pressure, such as mobile hydraulic equipment
In what applications do you see hydraulic fixed-displacement pumps?
Variable is because fixed creates a constant flow at a high pressure which means there is a higher electrical cost over time
Is the fixed or variable displacement pump more electrically efficient? Why?
- high - 10,000
Radial piston pumps are _____-pressure hydraulic pumps, capable of operating at _______ psi.
low-pressure applications
Unbalanced vane pumps are typically used in what?
- centrifugal force - mechanical means (such as a spring)
What 2 ways do the vane pumps extend their vanes?
1. As the drive gear rotates, it turns the driven gear. This causes both gears to move away from the inlet. This movement creates a vacuum on the inlet side of the pump as the gear teeth pull apart. The atmospheric pressure then pushes the fluid from the reservoir into the inlet. 2. As both gears rotate away from the inlet, the gear teeth move closer to the pump housing internal wall. This traps the fluid and forces it between the gear teeth and the internal wall toward the discharge. 3. As the gear teeth reach the outlet, they pull away from the internal wall. The fluid is then released. As the gear teeth start moving toward each other again, all fluid is forced out of the pump by decreasing volume. 4. As the gear teeth mesh back together, they form a seal that does not allow most of the fluid to flow back into the inlet. More fluid moves into the outlet area each time fluid is forced out of the gear teeth. This forces the fluid through the outlet port and into the hydraulic system
What 4 steps do the external gear pumps operate in?
adjusting a cam ring
What allows the volume per revolution to change according to system pressure in a variable-displacement, pressure-compensated vane pump?
in mobile and industrial applications such as hydraulic log splitters, shear presses, underground well drilling ma- chines, and trash compactors
What applications are double or triple pumps mostly used in?
pneumatic applications or to move products such as slurries, pastes, and solids, pulp and paper processing chemical refining, food and beverage processing, pharmaceutical production, and biotechnology.
What applications are lobe pumps usually used in?
where a large amount of varied pressure is required such as backhoes, hydraulic cranes, heavy-duty presses, and balers, used where heat buildup can affect pump performance.
What applications are seen with pressure-compensated variable- displacement inline axial piston pump?
1. The offset rotor rotates with vanes contacting the cam ring, creating a vacuum at the inlet of the pump. As the rotor rotates, the vanes extend outward by centrifugal force, creating a confined space for the fluid. The shape of the inlet allows the pump to pull more fluid into the confined space. 2. As the fluid becomes trapped between the vanes and the cam ring, it is forced toward the outlet of the pump. 3. As the trapped fluid gets closer to the outlet side of the pump, it is released from its confined space. The outlet is also shaped to allow more fluid to move through the pump. At this point, the vanes are forced back into the rotor by the cam ring, making a smaller confined space for the fluid. 4. As the fluid is forced out of the confined space, the rotor and the cam ring provide a leakproof seal that does not allow the fluid to slip back to the inlet. At the same time, more fluid is forced out of the pump, forcing fluid into the system.
What are 4 basic steps on how unbalanced vane pumps operate in four basic steps?
- ease of maintenance - good suction characteristics - quiet - efficient - operate at temperatures ranging from -25°F to 500°F
What are advantages for vane pumps?
gear, vane, and piston pumps
What are different types of hydraulic pumps?
unbalanced vane pumps, variable-displacement pressure-compensated vane pumps, and balanced vane pumps.
What are different types of vane pumps?
stainless steel
What are nameplates usually made of?
- prolong the life of the shaft bearings - allows the pump to run at higher speeds and at higher pressure ratings than an unbalanced vane pump
What are some advantages of a balanced vane pump?
simple design, reliable, and durable
What are some advantages of a pressure-compensated variable- displacement inline axial piston pump?
- pump fluids with a wide range of viscosity - operate at temperatures up to 750°F - reliable - easy to maintain
What are some advantages of internal gear pumps?
can operate under a wide range of pressures, have high-pressure capability, can operate in a wide range of environments, and can be small to large in size
What are some advantages of positive-displacement pumps?
• low cost • ability to handle dirt better than other types of pumps • easier to repair than other pumps • can be used with a wide range of hydraulic fluid viscosities • reduced sensitivity to pump cavitation • low noise levels • output that is more predictable because it is linear with the speed of the prime mover.
What are some advantages of using gear pumps?
high- pressure devices, such as large press machines, and heavy-duty construction and industrial equipment
What are some applications for piston pumps?
creating hydraulic flow for hydraulic press equipment, agricultural equipment, construction equipment, flight navigation systems, and robotic systems
What are some applications for positive-displacement pumps?
- not as efficient as other types of pumps - have fixed clearance ends - can only accomplish volume control by changing the pump gears or changing the speed of the prime mover
What are some disadvantages of using gear pumps?
- a frame, gears, housing, and a shaft - O-rings, backup rings, and seals
What are some major parts for a gear pump assembly? What are some minor parts?
compensated, load sensing, torque or horse- power limiter, and electronic displacement
What are some of the most common types of displacement control methods
mobile and industrial equipment where a high-pressure rating is required and space is limited
What are some typical applications for bent-axis piston pumps?
equipment that uses a heavy fluid for low fluid flow and high pressure, such as plastics injection molding machines or die-casting machines for metals
What are some typical applications for radial piston pumps?
industrial production facilities and in automotive automatic transmissions
What are some typical uses of internal gear pumps?
fixed and variable
What are the 2 categories for positive-displacement pumps?
cam or rotating piston pumps
What are the 2 classifications for radial piston pumps?
positive-displacement and non-positive displacement (dynamic) pumps
What are the 2 main categories for hydraulic pumps?
variable and fixed displacement
What are the 2 options for piston pumps?
1. Fluid enters the inlet port between the inner rotor and outer rotor. 2. Fluid travels through the pump between the teeth of the two rotors. 3. The inner rotor and outer rotor teeth mesh to form a seal between the in- let and outlet ports, forcing the fluid through the outlet port.
What are the 3 basic steps for gerotor pumps?
1. As the motor turns the external toothed gear, the gear teeth unmesh, creating an increasing volume. Atmospheric pressure then pushes the fluid from the reservoir into the inlet of the pump. 2. The fluid becomes trapped in the cavities of the unmeshed gears. As the gears rotate, the crescent seal separates the internal gear and the external gear. The fluid continues to move as the two gears continue to rotate. 3. As the two gears reach the end of the crescent seal, the gears begin to mesh again, decreasing the volume. The decrease in volume forces the fluid out of the cavities between the teeth and causes the fluid to flow through the outlet side of the pump and into the hydraulic system
What are the 3 basic steps for internal gear pumps?
1. As the drive shaft rotates, the piston block rotates in the same direction. This pulls a piston from the number of pistons out and creates suction. The piston is pulled because it is attached to the swash plate and the swash plate is in a fixed, slanted position. The farther back the piston moves, the more volume of fluid it will move. The length of the piston is the main determinant to the amount of gpm a pump can produce. 2. As the piston moves through the first half of the pump, it pulls more fluid every degree it turns, trapping more fluid in the piston barrel. 3. When the piston reaches the halfway point of a cycle (180°), the piston pushes fluid out of the piston barrel. As the shaft continues to rotate, more fluid is forced out of the piston barrel. 4. As the piston completes a 360° cycle, all fluid is pushed out of the piston barrel, creating a leakproof seal that will not allow the oil to reenter the inlet. At the same time, the next piston forces fluid out of its barrel, which forces fluid flow in the hydraulic system
What are the 4 basic steps that axial piston pumps operate in?
1. As the lobes unmesh, they create a vacuum by increasing the volume on the inlet side of the pump. 2. The fluid flows into the pump housing and is trapped by the lobes as they rotate. 3. The fluid travels around the interior of the pump housing in the gaps between the lobes and starts to leave the trapped areas. 4. The meshing of the lobes forces the fluid through the outlet into the system.
What are the 4 basic steps that lobe pumps operate in?
1. The pump creates a vacuum by increasing the volume at its inlet, which is connected to the reservoir. Vacuum is created in a confined space that has less pressure than atmospheric pressure. The vacuum in a pump is created when the pump rotates and an increased volume is created at its inlet. The pressure in the tank is at atmospheric pressure, which is higher than the vacuum created at the inlet. Atmospheric pressure forces the fluid to flow from the tank into the inlet of the pump./ 2. Once the fluid enters the pump through the inlet, the pump traps the fluid through a sealing method. A seal is an airproof and/or fluidproof joint between two members. The fluid travels through the pump, in decreasing volume, towards the outlet side of the pump./ 3. Once the trapped fluid moves toward the outlet side of the pump, the sealed chamber opens, decreases its volume, and releases the fluid into the pump outlet./ 4. The sealed chamber then closes, preventing fluid in the outlet side of the pump from slipping to the inlet side of the pump. At the same time, more fluid is forced out of the outlet and into the hydraulic equipment.
What are the 4 basic steps that positive displacement pumps operate in?
external, lobe, internal, or gerotor pumps
What are the different types of gear pumps?
inline axial, bent axial, variable-axis, variable-bent-axis, radial, and variable radial piston pumps.
What are the different types of piston pumps?
Hydraulic pump ratings, determined by the pump manufacturer
What are the main factors in determining pump use? How is this determined?
displacement, gallons per minute, pressure, and volumetric efficiency
What are the most common pump ratings?
gear and vane pumps
What are the most common types of double and triple pumps?
electric motors and internal combustion engines
What are the two main types of prime movers used in fluid power systems?
The resistance to fluid flow in the pathway and the load on the system
What creates pressure in a hydraulic system?
the angle at which the pistons and piston block are set
What determines the amount of fluid flow within a bent-axis piston pump?
service the pump quickly because it allows for replacement of the entire assembly when the internal parts need to be replaced
What does a cartridge assembly allow a technician to do?
timing gears
What does a lobe pump require in order to drive the lobe-shaped driven gears?
susceptible to problems with dirt
What is a disadvantage of gerotor pumps?
The design of their pistons and barrel allows for a short stroke.
What is one of the main reasons a radial piston pump is used?
- that one prime mover is used to rotate two or three pumps at the same time - can provide greater flow by connecting the pumps in series - they can supply two or three different hydraulic systems using only one prime mover
What is the advantage of using double or triple pumps?
- high cost - if you beaks down, the whole system shuts down
What is the disadvantage of using double or triple pumps?
D = rpm x D (cu in.) D = 1120 rpm x 1.94 cu in = 2173 cu in./min
What is the displacement of a pump with revolutions of 1.94 cu in. that has a prime mover with revolutions of 1120 rpm?
Q = (cu in/rev * rpm) / 231 Q = (4 cu in/rev * 1725 rpm) / 231 = 29.87
What is the gpm of a pump that has a displacement of 4 cu in. that operates at 1725 rpm?
the two lobes do not have to make contact with each other, thereby reducing the amount of operational noise and wear on the pump
What is the main advantage of having two driven lobes? Why?
through internal pilot pressure.
What is the most common method to vary the angle of a swash plate in a pressure-compensated variable- displacement inline axial piston pump?
bent-axis piston pump
What is the most durable type of hydraulic pump and can operate at pressures of up to 10,000 psi?
replace its meshing gears with those of a different size
What is the most practical method used to change the flow of a gear pump?
1. Remove the pump from its motor coupling by removing the bolts; 2. Remove all bolts from the front of the pump that hold the pump assembly together; 3. Disassemble pump; a. Detach the front plate assembly from the pump; b. Remove the two gears from the body housing; c. Detach the body housing from the back plate assembly; 4. Place all parts in a straight line in the exact order that they were disassembled; 5. Inspect all seals that connect the three main sections together; a. If the seals are good, proceed to step 6; b. If the seals are worn or damaged, replace them; 6. Inspect the ball bearings for wear and lubrication. Replace or regrease as required; 7. Replace the two gears with new gears in the order that they have been laid out; 8. Reassemble the gear pump by working backwards from step 7;
What is the procedure for replacing two gears in a gear pump
1. Connect the outlet side of the pump directly to a pressure gauge. 2. Turn the pump ON and record the pressure when the pump rotor becomes centered. 3. Use the pressure adjustment screw to set the desired fluid flow.
What is the procedure for setting the maximum fluid flow of a variable-displacement, pressure-compensated vane pump?
Eff(v) = (P(o) / P(ro)) * 100 Eff(v) = (19 gpm / 20 gpm) * 100 = 95%
What is the pump efficiency of a pump rated for 20 gpm that has actual output of 19 gpm?
- Built with the pistons lying flat and facing inward toward the shaft; - The inlet and outlet are located close to the shaft - The piston block is off-center inside the cam ring.
What makes the radial piston pump different than the axial piston pump?
the rpm of the prime mover
What must remain fixed within a variable displacement pump?
low-to moderate-pressure hydraulic applications of less than 1000 psi, such as trash compactors, hydraulic lifts, and hydraulic elevators
What type of applications are gerotor pumps used in?
Load sensing
What type of displacement control method controls a variable displacement pump by sensing an increase of a load in the system by monitoring the pressure drop across an orifice. If the load side pressure of the orifice increases, the pump varies the displacement of the pump to increase the pressure on the supply (pump) side of the orifice.
Electronic control
What type of displacement control method controls the displacement of a pump using an electrical signal and is accomplished with either a proportional or a servo attachment.
Torque or horsepower limiter
What type of displacement control method varies the displacement to maintain a constant horsepower or torque input when the speed of the prime mover does not change
dirty environments
What type of environment is ideal for gear pumps?
Positive-displacement
What type of pump is the only type of pump used in hydraulic systems and equipment?
Dynamic because they cannot create flow against the pressures found in hydraulic systems
What type of pumps are rarely used for hydraulic applications? Why?
a cam pump
What type of radial piston pump has a rotating internal cam that moves the pistons in cylinders?
rotating piston pump
What type of radial piston pump has pistons that are housed in a rotating piston block that is offset inside the pump housing and rotates around a fixed shaft?
elliptical cam ring
What type of ring does a balanced vane pump have?
As pressure increases, the compensator spring is compressed until concentricity on the compensator ring is achieved. It produces no more flow, resulting in no power loss and no fluid heating
When is maximum pressure achieved in a variable-displacement, pressure-compensated vane pump?
in low volume transfer applications such as hydraulic aerial lifts, log splitters, dump trucks, trailers, earthmovers, trucks, buses, and machine tool equipment.
Where can gear pumps be found?
nameplate with model number, manufacturer name, and serial number
Where is information for pumps found?
Unbalanced vane pump
Which vane pump has the simplest design?
because they have less initial cost
Why are fixed-displacement pumps more economical than variable-displacement pumps?
A high pressure differential between the inlet and outlet of the pump creates a load on the rotor that is attached to the shaft.
Why do unbalanced vane pumps have larger bearings and shafts that must be used?
It is used to ensure smooth movement and correct placement of the cam ring
Within a variable-displacement, pressure-compensated vane pump, what does a thrust block do?
cartridge assembly
a cartridge located in a vane pump that houses the vanes, rotor, and cam ring, which are all placed between two end plates
crescent seal
a crescent-moon-shaped seal between the gears and between the inlet and outlet sides of an internal gear pump
prime mover
a device that supplies rotating mechanical energy to a fluid power system
unbalanced vane pump
a fixed- or variable-displacement hydraulic pump in which the pumping action occurs in the chambers on one side of the rotor and shaft
internal gear pump
a gear pump that consists of a small external drive gear mounted inside a large internal spur gear (ring gear)
external gear pump
a gear pump that consists of two externally toothed gears that form a seal within the pump housing
gerotor pump
a gear pump that has an inner rotor that meshes with the gear teeth of an outer rotor.
piston pump
a hydraulic pump in which fluid flow is produced by reciprocating pistons
gear pump
a hydraulic pump that consists of gears that mesh together in various manners to create fluid flow
vane pump
a hydraulic pump that creates a vacuum by rotating a rotor inside a cam ring while trapping fluid between vanes that expand and retract from the rotor while moving the fluid toward the output
- Cavitation - high shrieking sound or a sound similar to loose marbles or ball bearings in the pump
a localized gaseous condition within a stream of fluid, which occurs when pressure is reduced to vapor pressure. What is an indication of it?
- Gallons per minute (gpm) - Q = (cu in/rev * rpm) / 231
a measure of fluid flow that is used to measure small volumes of intermittently flowing fluids such as pump discharges. What is the equation?
hydraulic pump
a mechanical device that changes mechanical energy into hydraulic energy (fluid flow)
pressure-compensated variable- displacement inline axial piston pump
a piston pump in which the angle of the swash plate can be varied
bent-axis piston pump
a piston pump in which the pistons and cylinders are at an angle to the drive shaft and thrust plate.
radial piston pump
a piston pump that consists of a cylinder barrel, pistons with shoes, a ring, and a valve block located perpendicular to the pump shaft
inline axial piston pump
a piston pump that consists of pistons in a rotating piston block parallel to the drive shaft
variable- displacement pump
a positive-displacement pump that can have its flow rate (gpm) changed
lobe pump
a positive-displacement pump that has two external-driven, intermeshing, lobe-shaped gears
fixed- displacement pump
a positive-displacement pump where the fluid flow rate (gpm) cannot be changed.
variable- displacement, pressure-compensated vane pump
a pump that automatically adjusts the amount of volume it displaces per rotation by centering the rotor when the pressure in the system starts to build
balanced vane pump
a pump that consists of a cam ring, rotor, vanes, and a port plate with opposing inlet and outlet ports
positive-displacement pump
a pump that has a positive seal between its inlet and outlet and moves a specific volume of hydraulic oil with each revolution of the shaft
- 75,000 - 600 fps to 4000 fps
an air bubble exposed to a 5000 psi cavitation may create an implosion pressure of _______ psi and travel at a speed of ____ fps to _______ fps.
swash plate
an angled plate in contact with the piston heads that causes the pistons in the cylinders of a pump to extend and retract
Implosion
an inward bursting
- Pseudocavitation - low reservoir fluid, contaminated fluid, or leaking pump suction lines, inlet port of a pump is restricted, suction line is damaged, plugged, or collapsed, increase in pump rpm that requires more fluid than the system piping allows, fluids with an increased viscosity due to lower ambient temperatures, or an increase in the viscosity of a fluid in a system when the system has a long suction line - loud noise for an extended period of time
artificial cavitation caused by air being allowed into the pump suction line. How is it caused? How is it indicated?
Pressure rating
the highest amount of pressure at which a pump can continually create flow without premature wear
- Volumetric efficiency - Eff(v) = (P(o) / P(ro)) * 100 Eff(v) = volumetric efficiency (in %); P(o) = actual pump output (in gpm); P(ro) = rated pump output (in gpm)
the relationship between actual and theoretical fluid flow, or pump gpm What is the formula?
Displacement D = rpm x D (cu in.)
the volume of hydraulic fluid moved during each revolution of a pump's shaft, cubic inches per revolution. What is the formula?
