International Journal of Engineering Trends and Technology (IJETT) – Volume1 Issue2 – May 2011
Design of Pneumatic Quick Exhaust Circuit
Mr. ASHOKKUMAAR.A
Department of Mechanical Engineering,
Bharath institute of science and technology, Bharath University,
Chennai-600073,Tamilnadu
Abstract—Quick-exhaust valves (QEVs for short) are ready-made piston valves or diaphragm valves,
designed to quickly exhaust pneumatic cylinders. They work somewhat similarly to pneumatically
modified sprinkler valves, they are more expensive and harder to find, but also perform better. QEVs need
a separate pilot valve for triggering. They can be very sensitive, triggering at a pressure drop of a few psi,
so care should be taken when filling with a Schrader valve or other valves that will let out air when
disconnected. Most QEVs are designed to be filled from the pilot side, and will typically work well using a
3-way valve as the fill/pilot valve. Some QEVs will also work when filled from the chamber side. Small
QEVs are sometimes used as pilots for larger valves, often to allow the use of a blowgun as the trigger.
Keywords— pneumatics,QEVs
INTRODUCTION
QUICK exhaust valves are pressure-sensitive venting devices that are used with double-acting actuators
in on off applications where positioners are not required. When triggered, quick exhaust valves almost
instantaneously vent one side of the double-acting actuator to atmosphere, allowing the valve to move to
the full-closed or full-open position. Quick exhaust valves are installed between the air supply and the
actuator. As long as a normal air supply is provided to the actuator, normal operation continues. However,
when the air supply fails or is interrupted, the quick exhaust valve reacts to the significant differential
pressure. An internal diaphragm diverts the exhaust flow coming from the actuator through an enlarged
orifice, allowing the internal pressure of the actuator to vent much more quickly. A needle valve must be
installed parallel to the quick exhaust valve so that the trip point of the quick exhaust valve can be
adjusted, allowing it to react only to large signal demands.
Quick exhaust valves are especially helpful with on off applications, where exceptional stroking
speeds are required in both directions . Another common application for quick exhaust valves is when a
double-acting actuator with a positioned must provide a fast stroke in one direction.
Quick Exhaust Valve, a commercial piston or diaphragm valve in a metal body intended for the
quick venting of pneumatic cylinders. In spud gunning they are ideal barrel sealing valves with faster
opening times than custom piston valves and high flow rates. They can be commonly found in sizes from
⅛ inch to 1½ inches (3–40 mm) and sometimes even larger models. It provides an easy option for
inexperienced spud-gun builders but the cost is usually greater than for any other valve type.
PNEUMATICS- is a branch of technology that deals with the study and application of pressurized gas to
effect mechanical motion. Pneumatic systems are extensively used in industry, where factories are
commonly plumbed with compressed air or compressed inert gases. This is because a centrally located and
electrically powered compressor that powers cylinders and other pneumatic devices through solenoid
valves is often able to provide motive power in a cheaper, safer, more flexible, and more reliable way than
a large number of electric motors and actuators. Pneumatics also has applications in dentistry,
construction, mining, and other areas.
VALVE-is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or
slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe
fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from
higher pressure to lower pressure.
PNEUMATIC SYSTEMS- in fixed installations such as factories use compressed air because a
sustainable supply can be made by compressing atmospheric air. The air usually has moisture removed
and a small quantity of oil added at the compressor, to avoid corrosion of mechanical components and to
lubricate them.
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International Journal of Engineering Trends and Technology (IJETT) – Volume1 Issue2 – May 2011
Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is
commonly just air. Smaller or stand-alone systems can use other compressed gases which are an
asphyxiation hazard, such as nitrogen - often referred to as OFN (oxygen-free nitrogen), when supplied in
cylinders.
Any compressed gas other than air is an asphyxiation hazard - including nitrogen, which makes
up 77% of air. Compressed oxygen (approx. 23% of air) would not asphyxiate, but it would be an extreme
fire hazard, so is never used in pneumatically powered devices.
Portable pneumatic tools and small vehicles such as Robot Wars machines and other hobbyist
applications are often powered by compressed carbon dioxide because containers designed to hold it such
as soda stream canisters and fire extinguishers are readily available, and the phase change between liquid
and gas makes it possible to obtain a larger volume of compressed gas from a lighter container than
compressed air would allow. Carbon dioxide is an asphyxiant and can also be a freezing hazard when
vented inappropriately.
PNEUMATIC ACTUATORS-of which cylinders are the most common, are the devices providing power
and movement to automated systems, machines and processes. A pneumatic cylinder is a simple, low cost,
easy to install device that is ideal for producing powerful linear movement over a wide range of velocities,
and can be stalled without causing internal damage. Adverse conditions can be easily tolerated such as
high humidity, dry and dusty environments and repetitive clean down with high pressure hoses. The
diameter or bore of a cylinder determines the maximum force that it can exert and the stroke determines
the maximum linear movement that it can produce. Cylinders are designed to work at different maximum
pressures up to 16 bar. The pressure actually supplied to a cylinder will normally be reduced through a
pressure regulator to control the thrust to a suitable level. As an example of cylinder power, a 40mm bore
cylinder working at 6 bar could easily lift an 80kg man. The basic construction of a typical double acting
single rod cylinder is shown in the cut away section where the component parts can be identified.
Pneumatic actuators are made in a wide variety of sizes, styles and types including those giving a semi
rotary output. Each major type will be covered in concept.
LITERATURE REVIEW
Shengdun Zhao et al described a compound expansion-chamber muffler, which consists of a sound
absorbing chamber and a switch valve, the chamber integrating structural features of impedance muffler
and micropunch plate muffler, is proposed to diminish impulse exhaust noise of pneumatic friction clutch
and pneumatic friction brake (PFC/B) in mechanical presses. The structure decreases the impulse exhaust
noise of PFC/B over 30 dB(A). A one-dimensional flow model is applied to study the aerodynamic
characteristics of compound exhaust process of the single acting cylinder and muffler because the exhaust
time is a critical factor for application of muffler in PFC/B. The volume of sound absorbing chamber is
found to be an important design parameter to minimize the exhaust resistance of pneumatic cylinder.
Experiments are also conducted to validate analytical results. Then the effects of diameter of exhaust ducts
and volume of muffler on the exhaust time are discussed in detail. The proposed one-dimensional
computational method, which considers the coupling of air-flow field and sound field, gives satisfactory
results for the preliminary design of an expansion-chamber muffler. This method has been applied to an
existing model HKM3-40MN to reduce its impulse noise.
F.-J Wang et al explained that pneumatic transport of Group C 20 µm glass beads was studied in a 31.7
mm vertical line, along with 66 µm Group A glass beads for comparison. Pressure gradients along the
riser were measured and the Zenz type state diagrams were constructed for both type of particle. For Group
C particles, the results show that the Zenz diagram has the usual characteristic form, but the minimum
pressure gradient is much lower and is positioned at a significantly higher gas velocity. Multiple layers of
Group C particles were found to adhere to the column wall, while only a fraction of the column inner
surface was covered by the 66 µm particles. The effects of the electrostatics effect during solids conveying
was also examined through the addition of anti-static particles and was shown to be less significant for the
finer particles. This is because the tube inner surface is entirely covered by the particulates, which reduces
the charging since only like materials are then in contact.
J.A. Witz in his paper is concerned with the use of pneumatic compliances to control the heave, roll
and pitch motions of marine vehicles when disturbed by operational loads. The pneumatic compliances are
in the form of open bottom air tanks attached to the vessel at the water line and extending above and below
still water level. Each tank traps a volume of air above its internal water level. Active operation of these
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tanks involves controlling the amount of air trapped within the tanks. The air exerts varying forces and
moments on the vessel which may be used to counteract disturbing forces. This paper describes a time
domain method of dynamic analysis that is used to investigate the performance of such a system. Three
application studies are presented which involve the suppression of motion due to vessel loading and crane
operation on semisubmersible and monohull vessels.
BASIC COMPONENTS
BODY- The valve's body is the outer casing of most or all of the valve that contains the internal
parts or trim. The bonnet is the part of the encasing through which the stem (see below) passes and that
forms a guide and seal for the stem. The bonnet typically screws into or is bolted to the valve body.
Valve bodies are usually metallic or plastic. Brass, bronze, gunmetal, cast iron, steel, alloy steels
and stainless steels are very common. Seawater applications, like desalination plants, often use duplex
valves, as well as super duplex valves, due to their corrosion resistant properties, particularly against warm
seawater. Alloy 20 valves are typically used in sulphuric acid plants, whilst monel valves are used in
hydrofluoric acid (HF Acid) plants. Hastelloy valves are often used in high temperature applications, such
as nuclear plants, whilst inconel valves are often used in hydrogen applications. Plastic bodies are used for
relatively low pressures and temperatures. PVC, PP, PVDF and glass-reinforced nylon are common
plastics used for valve bodies.
BONNET- acts as a cover on the valve body. It is commonly semi-permanently screwed into the valve
body or bolted onto it. During manufacture of the valve, the internal parts are put into the body and then
the bonnet is attached to hold everything together inside. To access internal parts of a valve, a user would
take off the bonnet, usually for maintenance. Many valves do not have bonnets; for example, plug valves
usually do not have bonnets. Many ball valves do not have bonnets since the valve body is put together in a
different style, such as being screwed together at the middle of the valve body.
Ports are passages that allow fluid to pass through the valve. Ports are obstructed by the valve
member or disc to control flow. Valves most commonly have 2 ports, but may have as many as 20. The
valve is almost always connected at its ports to pipes or other components. Connection methods include
threadings, compression fittings, glue, cement, flanges, or welding.
DISC - valve member is a movable obstruction inside the stationary body that adjustably restricts flow
through the valve. Although traditionally disc-shaped, discs come in various shapes. Depending on the
type of valve, a disc can move linearly inside a valve, or rotate on the stem (as in a butterfly valve), or
rotate on a hinge or trunnion (as in a check valve). A ball is a round valve member with one or more paths
between ports passing through it. By rotating the ball, flow can be directed between different ports. Ball
valves use spherical rotors with a cylindrical hole drilled as a fluid passage. Plug valves use cylindrical or
conically tapered rotors called plugs. Other round shapes for rotors are possible as well in rotor valves, as
long as the rotor can be turned inside the valve body. However not all round or spherical discs are rotors;
for example, a ball check valve uses the ball to block reverse flow, but is not a rotor because operating the
valve does not involve rotation of the ball.
SEAT- is the interior surface of the body which contacts the disc to form a leak-tight seal. In discs that
move linearly or swing on a hinge or trunnion, the disc comes into contact with the seat only when the
valve is shut. In disks that rotate, the seat is always in contact with the disk, but the area of contact
changes as the disc is turned. The seat always remains stationary relative to the body.
Seats are classified by whether they are cut directly into the body, or if they are made of a
different material
1. HARD SEATS are integral to the valve body. Nearly all hard seated metal valves have a
small amount of leakage.
2. SOFT SEATS are fitted to the valve body and made of softer materials such as PTFE or
various elastomers such as NBR, EPDM, or FKM depending on the maximum operating
temperature.
BALL VALVE-A closed soft seated valve is much less liable to leak when shut while hard seated valves
are more durable. Gate, globe, and check valves are usually hard seated while butterfly, ball, plug, and
diaphragm valves are usually soft seated.
STEM- transmits motion from the handle or controlling device to the disc. The stem typically passes
through the bonnet when present. In some cases, the stem and the disc can be combined in one piece, or
the stem and the handle are combined in one piece.
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The motion transmitted by the stem may be a linear force, a rotational torque, or some combination of
these(Angle valve using torque reactor pin and Hub Assembly). The valve and stem can be threaded such
that the stem can be screwed into or out of the valve by turning it in one direction or the other, thus
moving the disc back or forth inside the body. Packing is often used between the stem and the bonnet to
maintain a seal. Some valves have no external control and do not need a stem as in most check valves.
Valves whose disc is between the seat and the stem and where the stem moves in a direction into the
valve to shut it are normally-seated or front seated. Valves whose seat is between the disc and the stem and
where the stem moves in a direction out of the valve to shut it are reverse-seated or back seated. These
terms don't apply to valves with no stem or valves using rotors.
CONTROL -Many valves are controlled manually with a handle attached to the stem. If the handle is
turned ninety degrees between operating positions, the valve is called a quarter-turn valve. Butterfly, ball
valves, and plug valves are often quarter-turn valves. If the handle is circular with the stem as the axis of
rotation in the center of the circle, then the handle is called a handwheel. Valves can also be controlled by
actuators attached to the stem. They can be electromechanical actuators such as an electric motor or
solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are
controlled by the pressure of a liquid such as oil or water. Actuators can be used for the purposes of
automatic control such as in washing machine cycles, remote control such as the use of a centralised
control room, or because manual control is too difficult such as when the valve is very large. Pneumatic
actuators and hydraulic actuators need pressurised air or liquid lines to supply the actuator: an inlet line
and an outlet line. Pilot valves are valves which are used to control other valves. Pilot valves in the
actuator lines control the supply of air or liquid going to the actuators.
The fill valve in a toilet water tank is a liquid level-actuated valve. When a high water level is reached,
a mechanism shuts the valve which fills the tank.
In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid
between the ports automatically controls flow through the valve.
5/2 DCV-The function of a directional control valve (DCV) is to control the direction of flow in a
pneumatic circuit. The DCV is used to start, stop and regulate the direction of air flow and to help in the
distribution of air in the desired line. When a pressure pulse is input into the pressure control port ‘P’, the
spool will move to the left, connecting inlet P and work passage Work passage ‘A’ will then make a
release of air throughR1 and R2. The directional valves will remain in this operational position until
signals of the contrary are received. Therefore, this type of directional control valves is said to have the
function of memory .
FLOW CONTROL VALVES- also known as volume control valves. It is used to regulate the volumetric
flow of the compressed air to different parts of pneumatic system. A flow control valves is metering valve
and check valve built in to one housing. In one direction, the air flow is restricted as it flows through the
metering valve in the other directions, it flow freely through the check valve. The metering valve and
check valve may be of several design. The air flow through the orifice is controlled by pointed needle. A
ball and spring check valve is used for free flow.
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SPEED CONTROL -For many applications, cylinders can be allowed to run at their own
maximum natural speed. This results in rapid mechanism movement and quick overall machine cycle
times. However, there will be applications where uncontrolled cylinder speed can give rise to shock
fatigue, noise and extra wear and tear to the machine components. The factors governing natural piston
speed and the techniques for controlling it are covered in this section. The maximum natural speed of a
cylinder is determined by:
• cylinder size
• port size
• inlet and exhaust valve flow
• air pressure
• bore and length of the hoses
• load against which the cylinder is working
From this natural speed it is possible to either increase speed or as is more often the requirement,
reduce it. First we will look at how the natural speed for any given load can be changed by valve selection.
Generally, the smaller the selected valve the slower the cylinder movement. When selecting for a higher
speed however, the limiting factor will be the aperture in the cylinder ports (Figure 22). Valves with flow
in excess of this limitation will give little or no improvement in cylinder speed. The aperture in the
cylinder ports is determined by the design. Robustly constructed cylinders will often be designed with full
bore ports. This means that the most restrictive part of the flow path will be the pipe fitting. These
cylinders are the type to specify for fast speed applications and would be used with a valve having at least
the same size ports as the cylinder. Lighter duty designs, particularly small bore sizes, will have the port
aperture much smaller than the port’s nominal thread size. This has the desired effect of limiting the speed
of the cylinder to prevent it from self destructing through repeated high velocity stroking. The maximum
natural speed of these cylinders can often be achieved with a valve that is oneor two sizes down from the
cylinder port size.
FRL UNIT-We have engaged ourselves in manufacturing and exporting a wide range of FRL unit
that is available with modular designs, filter regulator, pressure switches and lubricator units.
Manufactured utilizing high grade raw material, these frl units are fabricated with the help of our
engineers and designers using sophisticated technologies. These Air Filter Regulator Lubricators are
offered at competitive prices are extensively appreciated for sturdy construction, operation efficiency and
long service life. Moreover, we thoroughly test this unit on several parameters to ensure durability and
high performance
WORKING PRINCIPLE
In the circuit the two flow control valve one inlet line and other at the out line of the pneumatic
cylinder are used to regulate the speed of both the extending and retracting motion of the cylinder. The
motion and speed of a double acting cylinder can be controlled by using flow control valves. In
pneumatics, meter out flow control is preferred in all situations. The 5/2 DC valve is operated the air from
FRL moves to the flow control valve. The air opens the check valve and full amount of air is fed to the
blank end of the cylinder to make it forward stroke. The air from the earlier stroke in the rod side has to be
exhausted through the flow control valve. But check valve remains closed and there is only metered flow
through the metering valve. Thus speed of the double acting cylinder is controlled during forward stroke.
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The DC valve is not actuated that is in its spring mode, air flows to the rod side through check unit of flow
control valve. The exhaust air is controlled by metering valve of flow control valve. Thus speed of the
return stroke is controlled.
CONCLUSION
Our project is to design and fabricate a pneumatic quick exhaust circuit. The designed circuit
meets various demands both domestically and also used for industrial applications like mass production,
time saving operation and quality accuracy.
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