Hydraulic Circuit

In figure below hydraulic circuit for Milling Machine is shown. In Milling Machine cutter is situated at a fixed position and rotates with high speed. And the workpiece is clamped on table, which move linearly in to & fro motion. Table movement in milling machine is comparatively slower.  It has a main pump which is a low pressure and high discharge pump and one booster pump ,which boost the hydraulic pressure to higher level. By using a booster pump expensive high flow and high discharge pump is avoided. There are two set of flow control valve and check valves, fitted in both supply and return line of the cylinder to achieve speed control in both direction. A manually operated spool valve decides the direction of flow to the cylinder. The stroke length of the cylinder is adjustable through limit switches. The limit switch disconnect supply of oil to cylinder when table reaches the set position.

Hydraulic liquid  is pumped by a constant discharge pump into the direction control valve. It has four ports and three stages. If the pressure goes beyond desired limits, the same is released by the pressure relief valve. The liquid reaches the right side of the cylinder through the inlet E and outlet A of the valve. Due to the pressure of the liquid, the piston moves towards left. The tool head moves forward to perform the forward cutting stroke. The liquid on the left side of the piston is sent back to the reservoir through B and P. Due to the change of position of plunger inside the valve, the liquid reaches the left side of the cylinder through the inlet E and outlet B. Piston moves towards right. The tool head moves in the opposite direction and this movement is known as the return stroke. The liquid on the right side of the piston is sent back to the reservoir through A and P. Quick Return of the Ram Due to the change of stroke volume of the cylinder during ...

The basis for all hydraulic systems is expressed by Pascal's law which states that the pressure exerted anywhere upon an enclosed liquid is transmitted undiminished, in all directions, to the interior of the container. This principle allows large forces to be generated with relatively little effort.  The purpose of a specific hydraulic system may vary, but all hydraulic systems work through the same basic concept. Defined simply, hydraulic systems function and perform tasks through using a fluid that is pressurized. Another way to put this is the pressurized fluid makes things work. The power of liquid fuel in hydraulics is significant and as a result, hydraulic are commonly used in heavy equipment. In a hydraulic system, pressure, applied to a contained fluid at any point, is transmitted undiminished. That pressurized fluid acts upon every part of the section of a containing vessel and creates force or power. Due to the use of this force, and depending on how it’s app...

Speed control circuits . Speed control of Pneumatic Cylinders can be conveniently achieved by regulating the flow rate supply or exhaust air. The volume flow rate of air can be controlled by using flow control valves which can be either two way flow control valve or one way flow control valve There are two types of throttling circuits for double acting cylinders:  i) Supply air throttling ii) Exhaust air throttling Supply air throttling .  This method of speed control of double acting cylinders is also called meter –in circuit (Figure a) . For supply air throttling, one way flow control valves are installed so that air entering the cylinder is throttled. The exhaust air can escape freely through the check valve of the throttle valve on the outlet side of the cylinder. There is no air cushion on the exhaust side of the cylinder piston with this throttling arrangement. As a result, considerable differences in stroking velocity may be obtained even wit...