Control Valves used in the hydraulic system

Introduction to control valves

In a general layout of the hydraulic system, after the pump, the next important components are present which are control valves. They are generally placed in between the pump and actuators.

The pump generates a flow of oil which is fed to the actuators through a controlling element known as a valve. Basically, the valve is nothing but a device that controls the oil energy.

 

Need for control valves

1.     For blocking/stopping of flow of oil.

2.     To control the direction of flow.

3.     To control the pressure of oil.

4.     To control the flow quantity.

5.     Other special functions such as controlling the oil flow in one direction, diverting the flow, etc.

Classification of control valves

1.    According to construction

a)    Seat valves:

The seat valve consists of a poppet that sits on a specially machined and finished seat. The poppet is either a ball or cone mounted with the help of spring. The position of the poppet from the seat helps to operate the valve. The seat valves are used for pressure control or flow control of compressed air. Valve finishing is difficult and costlier and wear and tear of the valve area is not uniform

a)    Spool valves:

The spool valve consists of a sliding spool like a small piston sliding inside a finely finished bore in the valve housing. Its construction is simple and the position of the spool connects or disconnects the ports of the valves. It is used for direction control valves and the spool is loaded with the help of a spring. Valve bore and spool finishing is easier and simple and uniform wear and tear of valve spool and bore.

2.    According to the control parameter

a)    Pressure control valves:  

As its name suggested this type of valve is used to control the pressure energy of oil. Pressure control valves are classified according to their function, type of connection, size, and pressure operating range. Commonly used pressure control valves are as follows:

Sr. No	Type	Function
1.	Pressure relief valve	To relieve excessive pressure in the system
2.	Pressure reducing valve	To reduce the pressure of oil in a certain portion of a circuit
3.	Unloading valve	Unload the pressure in the system
4.	Sequence valve	To actuate actuators in a sequence

b)    Direction control valve:

This type of valve according to its name we can say it is used to change the direction of oil in a hydraulic circuit according to requirement. To operate the forward and backward motion of the actuator, the direction control valve is the main element. There are various types of direction control valves available in the market such as poppet type, spool-type, and DC valve according to a number of ports and positions for example 3/2 DC valve, 4/2 DC valve, 4/3 DCV, 5/3 DCV, etc.

c)    Flow control valve:

    In the hydraulic system, sometimes it is required to increase or decrease the speed of the hydraulic actuator as per application, e.g. In a hydraulic shaper, the return stroke is faster than the cutting stroke, similarly speed control is necessary for drilling and tapping operation. Thus, by varying the flow rate (Q) of the oil, we can change the speed of actuators. This function is performed by a flow control valve

d)    Non return valve/ Check valve:

The valve which allows the flow of oil in only one direction and does not allow reverse flow of oil is known as a check valve.

3.    According to the method of control

a)    Direct controlled valve:

The direct-controlled valves are generally normally closed valves. Its actuation is generally taking place according to the oil pressure and spring force. When oil pressure is less than the spring force then the valves are in the closed position. When the oil pressure is more than that of the spring force then the valve is get actuated and control over the oil flow is get takes place.

 

b)    Pilot operated valve:

When the valve element is actuated indirectly through the internal pilot line to relieve the excessive pressure it is known as pilot operated pressure relief valve

The pilot-operated valve is a self-contained system that does not require any external pressure source. The pilot valve, using system media and pressure, automatically controls the cylinder/motor pressure to either open or close the main valve depending on the pressure setting of the pilot vs the actual system pressures.

Conclusion

In this, we have covered all the necessary information related to hydraulic control valves used in the industry. From this blog, we are able to conclude that in the hydraulics market, you can find different types of hydraulic valves by different manufacturers designed to do different things in different applications. Some hydraulic applications require an individual valve, whereas more complicated hydraulic systems could use a combination of valves to complete their function. According to the type of application, the user has to select the appropriate valve.

Presented By:

32. Karan Misal

35. Madhav Mokashi

42. Pranav Nandedkar

49. Prathmesh Nikte 

50. Vaibhav Nipunage

Guided By:

Prof. Dr. S.P. Komble