The principal of close centre hydraulic systems is to provide oil flow on demand it enables simultaneous operation of many users connected to one pump. These systems almost always use variable flow piston pump with swash plate. There are few exceptions where gear pump is used with special LS dump wale These systems offer significant benefits in reducing engine power loss if compared with open centre systems where full capacity of the pump, almost always gear pump, is continuously pumped round the hydraulic circuit even when it is not operated. So how does it work? Well the swash plate changes its angle in relation to the piston head therefore reduces or increase the stroke of the pistons. Longer stroke means more output from pump.The swash plate is controlled with load sensing line. There are some different methods used to control the tilting of the swash plate so I will describe the most common used ,basically they are all the same. Tilting of the swash plate is done with force of a spring, working against the spring is a hydraulic operated piston controlled with valve this valve works with the pressure in the Load sensing line .The LS line. There are always 3 hydraulic lines the power line, return line and Load sensing line to every spool wale in these systems, the spool Wales operates hydraulic cylinders to lift up loaders or to control hydraulic motors, hydraulic trailer brakes etc. Now lets imagine you are going to start your machine engine is not running so the swash plate is fully tilted for max output because there is no pressure on the control piston. Now you start the engine oil flow starts out the power line the P line it goes to all the Spool valves in your machine trough them out return line the RT line to gallery Nothing is operated so pressure builds up behind the control piston forcing the swash Plate back but not all the way back a small pressure builds up in the LS line. Enough to keep the system live a small displacement of the swash plate generates so galled standby pressure usually around 20 to 40 bar . Now you want to lift up the front end loader on your machine you pull the lever for that spool valve the spool moves up in its bore and as it does it closes on the oil flowing trough the spool out the RT line ,opens to the hydraulic cylinders for loader and simultaneously to the LS line, pressure rises in LS line forcing valve for the control piston to move and when it does it unloads the pressure behind the control piston and the Spring force then tilts the swash plate .You now have full operating pressure usually around 190-230bar depends on machine manufacturer and enough flow for this movement .Now lets say you have to operate hydraulic trailer brake at the same time As you are lifting the front end loader you press your brake pedal down and that courses The spool in the trailer brake valve to move to close the RT line, opens to brake cylinders in trailer and to LS line ,the valve for the control piston receives more pressure so it moves further thus unloads more from control piston swash plate tilts more and there you Have Oil Flow on Demand. Category:Home › Autos • Will the trend toward economy-size car models lead Americans back to buying smaller-sized cars? — part 2 • You should never use after-market auto parts when maintaining or fixing your car • Should a new car be rust-proofed? • Will the trend toward economy-size car models lead Americans back to buying smaller-sized cars? — part 1 • Five safest cars in North America • How to ensure your teen drives safely after getting a license • Pros and cons of using an hydrogen generator for your car • DIY automotive maintenance: How to change the oil