Objective of the Program: Prepare the Students for Developing and Using Computer Technology

Basic Hydraulics

Module 4: Flow Control Valves & Pressure Relief Valves

PREPARED BY

Academic Services

January 2012

ATM 1122–Basic Hydraulics

Module 4: Flow control valves and pressure relief valves

Module Objectives

After the completion of this module, thestudentwill be able to:

Explain the functions of flow control valves.
Distinguishbetween the different types of flowcontrol valves
Identify the symbols of different flow control valves
Explain the function of Pressure relief valve.
Identify the symbol of a Pressure relief valve.
Simulate a hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve.
Explain the operation of the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve
Assemble the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve

Module Contents

Module Objectives

1Flow Control Valves:

1.1The one way flow control valve

1.2Two way flow control valve

2Pressure Control Valves

2.1Pressure relief valve

3Practical Task I

4. Practical Task II

4.1 Embossing machine

3.2Procedure of solution:

References

ATM 1122–Basic Hydraulics

1Flow Control Valves:

The flow control valve is used to control the speed of a cylinder or a motor by controlling the amount of fluid flow rate passing through it.

As explained in Module 1, the flow rate is the volume of fluid that moves through the system in a given period of time. Flow rates determine the speed at which the output device (e.g., a cylinder) will operate. The flow velocity of a fluid is the distance the fluid travels in a given period of time which is the extension speed of the cylinder.

: Extension velocity of a cylinder ()

: Flow rate ()

: Area ()

1.1The one way flow control valve

Theone way flow control valve (Fig.4.1.a) is used to control the flow rate in the hydraulic circuit only in one direction (throttling part: from A to B), and allowsa freeflow in the opposite direction (from B to A). Throttling is achieved by adjusting the valve screw
The ISO symbol of this valve is shown in Fig.4.1.b. /
(a) one way flow control valve

(b) ISO symbol of the one way flow control valve
Fig.4.1: (a) One way flow control valve.
(b) ISO symbol of one way flow
control valve
.

1.2Two way flow control valve

The two way control valve (Fig. 4.2) provides a constant flow rate in the case of variable loads.
This valve has two ports (A) and (P) and adjustingthrottle screw. The ISO symbol of this valve is shown in Fig.4.2.b /
Fig 4.2 (a)Two way flow control valve

Fig 4.2 (b) ISO symbol of two way flow control valve

2Pressure Control Valves

These valves are used to controland regulate the pressure in the hydraulic system.

2.1Pressure relief valve

Pressure relief valve (Fig.4.3.a) is used mainly as safety valve. It prevents the maximum permissible pressure in the hydraulic system from being exceeded. If the maximum pressure is reached at the valve inlet, the valve outlet is opened and the oil will flow out to the tank. The valve remains open until the built-in spring closes it after reaching the preset pressure in accordance with the spring characteristic.
The ISO symbol of the pressure relief valve is shown in Fig.4.3.b
where:P: input pressure,
T: tank port /
(a)Pressure relief valve

(b)ISO symbol of the pressure relief valve
Fig.4.3: (a) Pressure relief valve.
(b) ISO symbol of the pressure relief valve

3Practical Task I

3.1Controlling the speed of a double acting cylinder using a two way flow control valve.
Background:
The function of a two way flow control valve is to maintain a constant speed of the actuator under variable loads.
Required components:
SR / Name / Qty
1 / Double acting cylinder / 1
2 / Two way FCV / 1
3 / Check valve / 1
4 / 4/2 way valve / 1
5 / Power pack / 1

Fig 4.4 Shows a schematic diagram of the hydraulic circuit that controls the speed of a Double Acting Cylinderusing two way flow control valve.
Procedures
1- Prepare the components according to components list.
2- Install all components according to hydraulic circuit shown in Fig 4.4 (All components should be firmly fixed).
3- Connect hydraulic hoses according to the hydraulic circuit, (Check that all return lines are plugged and all hose lines are firmly plugged in).
4- Check all parts are connected properly to each other.
5- The operating pressure should not exceed 20 bar.
6- Switch on the hydraulic power pack.
7- Start the circuit, then adjust the two way flow control valve and note what happens within the circuit.
8- Switch off the hydraulic power pack.
9- Make sure that the circuit pressure is zero (free of pressure).
10-Dismantle the circuit and tidy up.

4. Practical Task II

4.1 Embossing machine

A special machine is used to emboss graphic symbols on metal foil. The foil is fed through the embossing machine. The advanced motion of the stamp must be capable of being varied in accordance with the fed speed as shown in Fig.4.5 The return motion must always be executed as a rapid traverse.A One way flow control valve is used to control the speed of the stamp, while a pressure relief valve is used to prevent the weight of the stamp from pulling the piston rod out of the cylinder. A 4/2 way valve is used to switch between advance and return motion.

Fig.4.5Embossing machine sketch

3.2Procedure of solution:

1.Draw the hydraulic circuit diagram for the task.

2.Simulate the hydraulic circuit using FluidSim software.

3.Assemble the circuit practically and check its operation.

4.Write down your observations.

Work sheet

G11- Basic Hydraulics – Term-2

Name: ______Section:______

1-State the function of the one way flow control valve.

......

2- Draw the I.S.O. symbol of the one way flow control valve.

......

3- Name the main parts of the one way flow control valve.

......

4- Statethe function of thetwo way flow control valve?

......

5- Draw the I.S.O. symbol of the two way flow control valve.

......

6- Statethe function of pressure relief valve.

......

References

Festo Didactic hydraulic basic level textbook TP 501.
Oil Hydraulic Systems, S.R. Majumdar, 2003
Different websites.

Student notes

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Module 4: Flow control valves & pressure control valves 1