Hydraulic Facts & Intranet Assistance

Hydraulic is known in the mechanical world as oil powered but in fact the word is used in the physical sense including any fluid like property in an element, like water and so on.


Fluid is made to flow by the use of a pump, the fluid is held and allowed to flow through a conduit of tubing, hoses, pipes, that have a hollow area within the conduit itself.

Hydraulic Facts


A fluid will flow through tubes and pipes as a fluid pump shaft is rotated. A fluid pump that has a pump flow directly proportional to the rotation of the pump shaft is said to be a positive displacement pump.


These types of pumps pump the fluid through the tubes as the engine rotates and the system is termed open center. The open center hydraulic system has valving (control valve) that when the valve spool is in neutral (centered and no lever movement) the passages from pump flow are open to flow fluid back to the hydraulic reservoir. It takes engine rotation to produce fluid to flow through a system. A hydraulic system is a conduit in a loop that allows fluid to flow as the engine rotates the shaft of the pump from the pump outlet to the pump inlet.


The parts normally associated with the open center systems have internal gears inside the pump housing and is called a gear pump in the industry. The pumps are very durable and can operate with dirty conditions in the oil. 


Companies that were using the gear pumps in the early years started migrating to variable displacement piston pumps in order to make the machine use less fuel and break metal parts less.   

The piston type pumps are usually associated with a closed center system. This system blocks fluid from flowing through the control valve at the valve spools inlet and outlet ports. Ports are the hollow passages inside the control valve body allowing fluid to flow. The passages are closed so fluid cannot flow through them.



In a closed centered pressure compensated system (John Deere radial piston pump) the pump produces the maximum flow capability until the back pressure in the system changes the flow rate to minimum required by the John Deere manufacturer. That back pressure is called standby pressure, it is the pressure available for the operator to have power as soon as the control lever is pulled or pushed out of the neutral position.



The radial piston pump is termed that because the pistons pumping the fluid are positioned in a radial fashion around the shaft and perpendicular in relation to the rotational axis of the pump shaft. The pistons are moved outwards and inwards (centered to outward).



With this type of pump the pistons are said to be at full stroke.

NOTE: Full stroke is associated with a round metal piece called a piston and located within a cylinder or tube. The tube will hold a maximum or a minimum amount of fluid and in direct proportion to it's dimensional size and position of the moveable piston inside the bore of the tube or cylinder.