The Cylinder Block and Valve Plates of a Piston Pump
The cylinder block is the area that holds the pistons. It has axial bores in which the pistons reciprocate and is attached to a yoke that allows it to rotate.
The yoke is attached to the spherical joint/shoe plate at an angle that impacts the pump’s discharge. We can change this angle to modify the amount of fluid that is dispensed.
Pistons
The pistons fit into bores in the cylinder block and move linearly back and forth in a reciprocating motion to charge and discharge the cylinder space. The amount of cylinder space charged and discharged per stroke depends on the length of each piston’s stroke. The pistons are driven by the rotor and the swash plate.
Pistons are made from a durable alloy and can be produced by casting or forging. Casting is the simplest method, where the alloy is heated until molten and then poured into a mold. Forging is a more complex process, where the metal isn’t melted but instead is forced into a die at high pressure to make a stronger, more durable product. Today’s pistons are usually made from Airless pump bottle aluminum because it is tough and lightweight, yet can withstand the extremely high temperatures generated by hot engines.
The connecting rods linking the pistons to the crank are another important component. Modern high-compression engines require a lot more work from the pistons, and that puts more strain on the sticks connecting them to the crank. To handle the increased load, connecting rods are now manufactured with cracked big-end caps that reduce the mechanical stress on the piston pin when it reaches TDC and BDC. Piston-to-bore clearances are also getting smaller, requiring tighter tolerances. These improvements are enabled by better computer modeling and more precise manufacturing techniques, as well as ever-evolving forging processes that allow metals to withstand higher temperatures.
Shoe Plate
A piston pump uses a shoe plate to help the pistons fit into the chamber. The shoes can be either complex or simple, and both have advantages. The more complex shoe plates tend to be harder to damage and may provide a better seal, but the simpler design has its benefits as well. The simplest shoe plates are made of metal, but more advanced ones can be made of plastic or rubber. The shoe plate’s primary function is to prevent excessive wear from the friction between the piston and the cylinder block wall, but it also serves to control fluid flow and pressure.
When the piston reaches the top of its reciprocation cycle, commonly known as top-dead-center or TDC, the connection between the trapped chamber and the valve plate is closed. This is followed by a short time period during which the fluid in the chamber is vented through one of the valve plate’s semi-circular ports – the discharge port.
During the rise phase of the pump’s cycle, the fluid in the trapped chamber flows out of the discharge port and into the cylinder, where it is pressurized to the point that the piston moves downwards. This motion increases the pressure Airless pump bottle on the outlet valve, which opens and lets high-pressure liquid or gas out of the cylinder.
Swash Plate
As the swash plate oscillates, its piston chambers take oil from the inlet and discharge it to the outlet. This process generates a high frequency disturbance called “swash plate vibration” that affects the pump’s pressure pulsation. By modelling the swash plate kinematics and geometry using full FSIs, the vibration amplitude of the swash plate angle and the discharge pressure pulsation can be reduced to an acceptable level.
One end of the swash plate wears against a mating surface on a stationary valve plate, which has two semi-circular ports that allow inlet of the operating fluid and exhaust of the discharge fluid. The other end of the swash plate is attached to the shoeplate and biased by a spring. The swash plate, shoeplate and bias spring rotate together with the cylinder barrel.
During the rising portion of the reciprocation cycle, the swash plate moves away from the valve plate. This causes the swash plate to create a larger volume of space to trap the hydraulic fluid in the piston chamber. As the swash plate continues to precess about the cylinder block axis, it moves back toward the valve plate. This changes the depth of the space available to hold hydraulic fluid inside the piston barrel and repeats the cycle. The pump’s displacement is controlled by changing the angle of the swash plate, or its pitch. Increasing the pitch increases the length of each piston stroke, which results in more fluid being pumped per revolution. Similarly, decreasing the pitch decreases the length of each piston stroke and reduces the amount of fluid pumped.
Valve Plate
The valve plate in a piston pump is an essential part of the overall operation of this type of hydraulic system. It separates the working fluid from the intake and discharge ports. It also controls the stroke length of the swash plate. The swash plate is attached to the shoe plate at an angle, which determines how long the pump’s stroke is. This angle can be varied, allowing for a change in the pump’s discharge.
In axial piston pumps, the swash plate has two holes through which fluid can pass. These are known as damping holes, and they have an impact on the pump’s performance. One of the most important effects is on the pressure in the piston chamber, which can lead to overshoot and undershoot. Using multi-objective genetic algorithm optimization, we were able to find an optimal valve plate design that minimized these effects.
This is accomplished by ensuring that the ratio of the front side of the valve plate to the backside is equal within design tolerance limitations, and the masses are evenly distributed over the front and back sides of the plate. This allows the swash plate to move smoothly without increasing the noise level.
Another factor that influences noise is the contact between the valve plate and the barrel face. This can cause scorching, shallow or deep scratches or gouges on the barrel face and the valve plate depending on the amount of movement. This is often due to an influx of hydraulic fluid from the kidney ports, which is not easily prevented.
