KRW - Ketterman Rowland & Westlund
First, determine if you have an open or closed center system. Next, determine how much flow GPM) you need. Next, how many components cylinders, motors) are going to be powered by the pump. You also need the size of the mounting flange, the type and size of shaft, the type and size of ports and the direction of rotation when facing the shaft.
First, do you need a single or double acting cylinder? Next, what is the pin to pin distance when extended and retracted? Also, how much force do you need to move the load, do you need it move in a certain amount of time and how is the cylinder mounted.
A single acting cylinder only provides force one way most snow plow and telescopic cylinders are single acting). A double acting cylinder provides force when extending and retracting.
A pump converts rotational force on its shaft into pressurized oil to supply hydraulic components. Example: electric or gas motor turns pump shaft, pump supplies oil to a cylinder. Pumps generally have large suction port and a smaller pressure port.