Shuttle valve
Encyclopedia
A shuttle valve is a type of valve
which allows fluid
to flow through it from one of two sources. Generally a shuttle valve is used in pneumatic systems, although sometimes it will be found in hydraulic systems.
from a fluid
is exerted through an opening on one end it pushes the ball towards the opposite end. This prevents the fluid from travelling through that opening, but allows it to flow through the middle opening. In this way two different sources can provide pressure without the threat of backflow
from one source to the other.
In pneumatic logic a shuttle-valve works as an OR gate
.
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
which allows fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
to flow through it from one of two sources. Generally a shuttle valve is used in pneumatic systems, although sometimes it will be found in hydraulic systems.
Structure and function
The basic structure of a shuttle valve is like a tube with three openings; one on each end, and one in the middle. A ball or other blocking valve element moves freely within the tube. When pressurePressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
from a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
is exerted through an opening on one end it pushes the ball towards the opposite end. This prevents the fluid from travelling through that opening, but allows it to flow through the middle opening. In this way two different sources can provide pressure without the threat of backflow
Backflow (plumbing)
Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. It can be a serious health risk for the contamination of potable water supplies with foul water. In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl...
from one source to the other.
In pneumatic logic a shuttle-valve works as an OR gate
OR gate
The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...
.
Applications
A shuttle valve has several applications including:- The use of more switches on one machine: by using the shuttle valve, more than one switch can be operated on a single machine for safety, and each switch can be placed at any suitable location. This application is normally used with heavy industrial machineryHeavy industryHeavy industry does not have a single fixed meaning as compared to light industry. It can mean production of products which are either heavy in weight or in the processes leading to their production. In general, it is a popular term used within the name of many Japanese and Korean firms, meaning...
. - Winch brake circuit: a shuttle valve provides brakeBrakeA brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
control in pneumatic winchWinchA winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...
applications. When the compressor is operated the shuttle valves direct air to open the brake shoes. When the control valveControl valvesControl valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor...
is centred, the brake cylinderMaster cylinderThe master cylinder is a control device that converts non-hydraulic pressure into hydraulic pressure, in order to move other device which are located at the other end of the hydraulic system, such as one or more slave cylinders...
is vented through the shuttle valve, and the brake shoes are allowed to close. - Air pilot control: converting from air to oil results in locking of the cylinder. Shifting the four-way valve to either extreme position applies the air pilot through the shuttle valve, holding the two air-operated valves open and applying oil under air pressure to the corresponding side of the cylinder. Positioning a manual valve to neutral exhausts the air pilot pressure, closing the two-way valves, and trapping oil on both sides of the cylinder to lock it in position.
- Standby and emergency systems: compressorGas compressorA gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
systems requiring standby or purge gases capability are pressure controlled by the shuttle valve. This is used for instrumentationInstrumentationInstrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
, pressure cables, or any system requiring continuous pneumatic input. If the compressor fails, the standby tank—regulated to slightly under the compressor supply—will shift the shuttle valve and take over the function. When the compressor pressure is re-established, the shuttle valve shifts back and seals off the standby system until needed again.