Type of Spool: Hydraulic [PDF]

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Type of Spool Spool is of two types namely sliding and rotary. Sliding spool is cylindrical in cross section, and the lands and grooves are also cylindrical. Rotary valves have sphere-like lands and grooves in the form of holes drilled through the.



Spool valves regulate the flow of fluid in hydraulic systems. Valves like this slide back and forward to make fluid flow in either one direction or another around a circuit of pipes.



Hydraulic Spool Valve Basics



A hydraulic spool valve is a switching device used to control hydraulic devices. Spool valves are used in everything from automotive power-steering systems to cranes. A spool valve can



turn the flow of hydraulic fluid from a hydraulic pump to an actuator on and off by blocking off the route the fluid takes.



Hydraulic Spool Valve Structure A hydraulic spool valve is a cylinder inside a sealed case.



It usually has valves leading to pump and the tank on one side, and valves leading to one or more hydraulic devices on the other side. Pressure can flow into the valve from the pump into the hydraulic devices, or drain out of them back into a hydraulic storage tank. A controller moves the valve back and forth in its case to slide the spools into different positions. The position of the rotor will only allow the hydraulic fluid to flow in one direction to perform a specific task.



A spool valve is part of a hydraulic system that directs the flow of hydraulic fluid. The valve is made up of spools that rotate or slide to block and open channels in a hydraulic system.



Function  Spool valves direct the flow of fluid to and from other valves within a hydraulic system. A typical four-way spool valve has openings leading to and from another valve, as well as from the fluid pump and to the fluid reservoir.



Rotary Spool Valves  A rotary spool valve consists of a fixed tubular sleeve, within which is a rotating, x-shaped piece called the "core." This valve functions much like a revolving door, with each bend of the core functioning as a portal for hydraulic fluid to leave and enter the valve. Sliding Spool Valves



 Sliding spool valves are slightly more complex than rotary spool valves. In sliding spool valves, the spool is grooved



and slides in and out of position within the sleeve, alternately blocking and opening the fluid intake and outtake portals.



Application: Rotary Valve Power Steering



A power-steering system should assist the driver only when he is exerting force on the steering wheel (such as when starting a turn). When the driver is not exerting force (such as when driving in a straight line), the system shouldn't provide any assist. The device that senses the force on the steering wheel is called the rotary valve. The key to the rotary valve is a torsion bar. The torsion bar is a thin rod of metal that twists when torque is applied to it. The top of the bar is connected to the steering wheel, and the bottom of the bar is connected to the pinion or worm gear (which turns the wheels), so the amount of torque in the torsion bar is equal to the amount of torque the driver is



using to turn the wheels. The more torque the driver uses to turn the wheels, the more the bar twists. The input from the steering shaft forms the inner part of a spool-valve assembly. It also connects to the top end of the torsion bar. The bottom of the torsion bar connects to the outer part of the spool valve. The torsion bar also turns the output of the steering gear, connecting to either the pinion gear or the worm gear depending on which type of steering the car has. As the bar twists, it rotates the inside of the spool valve relative to the outside. Since the inner part of the spool valve is also connected to the steering shaft (and therefore to the steering wheel), the amount of rotation between the inner and outer parts of the spool valve depends on how much torque the driver applies to the steering wheel. When the steering wheel is not being turned, both hydraulic lines provide the same amount of pressure to the steering gear. But if the spool valve is turned one way or the other, ports open up to provide high-pressure fluid to the appropriate line.



Sliding Valve Hydraulic Cranes Joy sticks and foot pedals are connected to hydraulic hoses that connect various hydraulic rams to spool valves. The spool valve is connected to the hydraulic pump via a third hose that is placed between the two hoses that run from the spool valve to the hydraulic ram. When a joystick is pushed in one direction, it causes the valve to shut off one of the hydraulic hoses leading to the ram and open the other. Which way the joystick is pushed determines whether the piston in the hydraulic ram slides in or out. The spool-valve system lets the crane operator control