Proportinal Valve By Pratik Patil

8/4/2019 Proportinal Valve By Pratik Patil

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NATIONAL INSTITUTE OF TECHNOLOGY, KARNATAKA, SURATHKAL 1

A REPORT ON

PROPORTIONAL VALVE_______________________

SUBMITTED BY:

PRATIK PATIL

M. TECH., FIRST YEAR, MECHATRONICS.

NATIONAL INSTITUTE OF TECHNOLOGY, KARNATAKA,SURATHKAL


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TABLE OF CONTENT:

SR. NO. DESCRIPTION PAGE NO.

1 Introduction 3

2 Types Of Proportional Valve 4

3 Principle of Pascals Law 5

4 Cross Sectional View 65 Valve Representation 7

6 Applications 8

7 Application In Braking 9

7.1 Braking System WithoutProportional Valve

10

7.2 Mounting Of Valve In Braking System 11

7.3 Role Proportional Valve In Braking 12

7.4 Methods To Control Rear BrakePressure

14

8 References 18


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INTRODUCTION:

A name Proportional means this valve gives output in proportion

to the input. It is an open loop control valve that means thefeedback of valve opening or closing is not received. Thepressure or force control at outlet ports is maintained by theprinciple of Pascals Law.

A Proportioning Valve is a valve that works on the laws of fluidpressure to distribute input forces to one or more output lines. A

proportioning valve can increase or decrease forces for eachoutput, depending on the cross-sectional surface areas of thoseoutput lines. A simple example is an input tube with cross-sectional area A entering a chamber. Leading out of the chamberare two more tubes, one with cross-sectional area 3A and theother with area A/2. If a force F is applied to the fluid in the inputtube, the pressure in that tube will be F/A. Utilizing pressure laws,we find that each output tube will see the same pressure. Thismeans the output tube with area 3A will yield a force of 3F, andthe output tube with area A/2 will yield a force of F/2. Thus, if youapply a 10-pound force to the input, you will get forces of 30-pound and 5-pound, respectively, from the outputs. If you apply a10 N force to the input, you will get forces of 30 N and 5 N,respectively, from the outputs.

These valves are also called as Electro-Hydraulics as they can be

operated by solenoid that is by supplying electric power or bysensors or by manual switches and the fluid used isincompressible liquid such as oil. Thus they can control directionof flow and/or amount of the flow and even the pressure or forceswithin the system as discussed.
http://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Pound_forcehttp://en.wikipedia.org/wiki/Pound_forcehttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Valve


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TYPES OF PROPORTIONAL VALVE:

1. Flow control valves

2. Pressure reducing valve

3. Pressure relief valve

4. Directional control valve

In this report we are going to discuss about flow control

valve


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PRINCIPLE OF PASCALS LAW:

Within a fluid the pressure applied at different points is equal.

Figure 1

When pressure P1=F1/a1 is applied at right chamber theequal pressure P2=F2/a2 acts at right camber. That means a

small force F1 at one point can create a large force F2 atanother point (Figure 1).


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CROSS SECTIONAL VIEW:

Figure 2This is typical cross sectional view of the solenoidoperated proportional valve.

When the solenoid is operated, the torque motor rotatesand magnetic field generated. Due to this the strip is tiltedslightly as a result the piston connected by mechanicalconnection moves forward thus the opening of ports takes

place. The fluid flows from tank to supply port and viceversa as shown by arrows.


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VALVE REPRESENTATION:

A B

1 2

P R

4/3 VALVE:

FOUR PORTS:

One pressure port, two service ports and one exhaustport

THREE STATES:

When solenoid 1 is actuated then first state isachieved in which fluid from tank (port P) goes toservice port A, and from service port B comes backto tank through port R.

When solenoid 2 is actuated then second state isachieved in which fluid from tank (port P) goes toservice port B, and from service port A comes backto tank through port R.

In the normal position all the ports remain closed asshow.

The arrow mark on solenoid represents current canvary (keep in mind output will vary in proportion to input).


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APPLICATIONS:

Supply different force to front and rearwheels while braking

Light length control(% of gas mixing can be proportional to air

volume input)

Steam flow adjusted until the desiredtemperature at the exchanger outlet is reached


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APPLICATION IN BRAKING SYSTEM:

When diagnosing wheel lockup, one item you'll want toinspect is the brake proportioning valve. The brakeproportioning valve is used to balance front and rearbrake loads during periods of hard braking. When brakeis applied to the vehicle the passengers move forwardbecause of the vehicles motion. As a result the loaddistribution changes, more load acts on front wheelscomparing to the rear wheels. So one has to apply morepressure to front wheels and comparatively lesspressure to the rear wheels. Because if same pressureis applied then rear wheels get locked before frontwheels which results it skidding of rear wheels. To avoidthis proportional valve is used. The proportioning valveis usually mounted near the master cylinder. Brakepressure supply lines are routed from the master

cylinder through the proportioning valve, to the calipersor wheel cylinders. Some system designs willincorporate the proportioning valve into the mastercylinder outlet ports, to the rear wheels.

The proportioning valve in a vehicle's brake systemprovides a way to control how much and when brakepressure is applied to each axle set of the brake system.Located between the master cylinder and the rest of thebrake system, this component is the key to safe, reliablebrake system operation in all conditions.


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Braking system without proportionalvalve:

Figure 3

Here whatever pressure applied at master cylinder samepressure acts at both front and rear wheels.This can be prevented by mounting proportional valve justafter master cylinder as shown in Figure 3.


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MOUNTING OF VALVE IN BRAKING SYSTEM:

Figure 4In the Figure 4 there are two supplies from master cylinder on

either side of the valve. Two supply ports for front wheels (one

for left and one for right). While only a single supply to rear

wheels.

By changing the diameter or cross sectional surface area of

front and rear wheel supply port we can achieve different

forces at respective wheels. Thus pre-locking of rear wheels

is prevented by maintaining greater force to front wheels and

comparatively smaller to rear wheels.


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Benefits

o The benefit of having a proportioning valve in the systemis that you can control front to rear brake bias by reducingpressure to the rear brakes when system pressure is highduring rapid deceleration. This prevents premature rearbrake lock-up during times of heavy braking.

Types

o There are three types of proportioning valve in use today:master cylinder mounted, combination valve mounted andload sensing. Master cylinder mounted valves are locatedon the master cylinder and screwed into the fluid ports

between the master cylinder and the brake lines.Combination valve mounted valves are part of thecombination valve along with the pressure differentialswitch and the metering valve. This component is usuallymounted to the inner fender or frame, just below themaster cylinder. Load sensing proportioning valves arelocated in the rear of the vehicle on the frame. A lever

attaches the valve to the suspension.


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Function

o The proportioning valve is a spring-loaded device. As fluidpressure builds, the plunger in the valve begins to unseat.When pressure reaches the calibrated range, the spring iscompressed, and the plunger moves to block the fluidpassage. This prevents premature wheel lock-up. In a loadsensing valve, the same function applies; however, thearm attaching the valve to the suspension changes the

calibration of the valve to compensate for load. As the loadgets heavier and compresses the suspension, the amountof pressure supplied to the rear wheels is increased.


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METHODS TO CONTROL REAR BRAKE

PRESSURE:

Rear Brake Pressure Control

In general, there are three ways to deal with rearbrake pressure: leave it alone, make it proportionalto the front brake pressure, or control it in a waythat combines these two strategies.

Strategy 1: Leave it Alone

If no device were used to modify the rear brakepressure, then as shown in Figure A, the frontbrake pressure and rear brake pressure wouldalways be equal. Naturally, this is the easiest way

to deal with the issue, but in order to prevent rearbias under all conditions; the rear brake itself wouldneed to be absolutely tiny.


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Strategy 2: True Proportioning

True proportioning, as shown in Figure B, wouldresult in rear brake pressures being linearlyproportional to front brake pressures under all

conditions. Ironic as it may seem, proportioningvalves do not provide this kind of control, as theyare not the purely proportional devices their namewould imply.


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Combining Strategies

Conventional proportioning valves should really bereferred to as braking force regulators or brakepressure regulating valves. While their namemight imply true proportional control, in reality theyprovide a combination of the control found inFigures A and B. Up to certain pressures, thesevalves allow equal pressure to both the front andrear brakes (as in Figure A). However, once a


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preset pressure point is reached (600 psi in theexample), the rear brake pressure continues tobuild, but at a slower rate (or slope) than the frontbrake pressure (as in Figure B). Figure C displaysthis for us quite clearly.


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REFERENCES:

Brake Proportioning Valves, 14528 Bonelli St.

Industry, CA 91746.

Hydraulic and Pneumatic Actuators and their

Application Areas Elena Ponomareva, May 26, 2000.

ITI GmbH, Webergasse 1 C/2 . 01067 Dresden,

Germany .

Date post:	07-Apr-2018
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