GENERAL INTRODUCTION EXPLANATION OF CX SERIES Variable Pumps All of the CX Series Excavators use an open center hydraulic system, in that there is always an output flow from the hydraulic pump flowing through the system. The CX Series Excavators use a variable volume piston pump system to be able to fully use the engine horsepower available. As the system operating pressure increases, the flow gradually reduces, to maintain a constant horsepower load on the engine. The theory is that when very high pressures are required, speed isn't so important. The CX Series Excavators use a two- section variable displacement piston pump, to provide the flow required to operate the functions.
Variable pumps are used to allow the delivery of a higher flow rate at lower working pressures, and then allow the pump to reduce flow at higher pressures to keep from stalling the engine. The increased flow at lower pressures makes the machine cycle faster, to increase the overall efficiency of the machine. The engine horsepower required to drive a hydraulic pump depends on the flow delivered by the pump, as well as the pressure at which system is operating. There is a mathematical formula to calculate the pump drive horsepower, but a rule of thumb to visualize this, is that it requires approximately 1 engine horsepower to deliver 1 gallon per minute of oil at 1500 psi.
Therefore, it would require 25 HP to deliver 25 GPM at 1500 psi. If the pressure increases to 3000 psi, the requirement would be 50 HP. The CX Series Excavators have an automatic pump de-stroke feature that reduces pump flow to a minimum delivery when all control levers are in the neutral position. This is accomplished with a hydraulic pilot signal from the control valve. This system saves fuel and eliminates wasted engine and hydraulic power. The minimum flow delivery of the pumps increases with machine size and engine horsepower. Although the pump configuration and manufacturer varies, in principal, all of the pump control systems operate the same.
1 - 4 CX EXCAVATORS Pumps MODEL CX130 CX160 CX210 CX240 Max. pump flow X 2 32.4 gpm 36.2 gpm 53.1gpm 56 gpm Pilot pump flow 6 gpm 5.8 gpm 5.3 gpm 5.3 gpm Manufacture Uchida Uchida Kawasaki Kawasaki Configuration Tandem Tandem Tandem Tandem