Mechanical Valves

In engineering valves are categorized and defined as device used for controlling the flow of fluids (liquids, gases and sludge) in a pipe or other enclosure. This control is done by means of a movable element that opens, shuts, or partially obstructs an opening in a passageway.
Valves are generally represented in engineering diagram with a symbol of cross path. 


There are seven main types of Valves: globe, gate, needle, plug (cock), butterfly, poppet, and spool.

Globe valves are linear motion valves that work as a unidirectional valve, it thus have a movable element which may be a tapered plug or a disk that fits or seat into a ring seat in valves body normally a spherical shape; the disk may carry a replaceable rubber, Oaring or leather washer, as in a household water faucet or tap valves. there types of body design for globe valves which are

1. Angle globe valve
2. Wye design globe
3. Tee or Z 

 Angler Globe valves, is a modification of the basic Tee/Z design Globe valves. The ends of this Globe valve are at an angle of 90 degrees, and fluid flow occurs with a single 90 degrees turn. They have a slightly lower coefficient of flow than Wye-designed Globe valves. They are used in applications that have periods of pulsating flow because of their capability to handle the slugging effect of this type of flow.


 Wye Globe valves, is an alternative for the high pressure drop,
in Wye-designed Globe valves the Seat and stem are angled at approximately 45 degrees, which gives a straight flow-path at full opening and offer the least resistance to flow. They can be cracked open for long periods without severe erosion. They are extensively used for throttling during seasonal or startup operations. They can be rod through to remove debris when used in drain lines that are normally closed.


Tee\Z Globe valves these are the most common design type, with a

Z-shaped diaphragm. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This design has the lowest coefficient of flow and higher pressure drop. They are used in severe throttling services, such as in bypass lines around a control valve. Tee-pattern Globe valves may also be used in applications where pressure drop is not a concern and throttling is required

Schematic diagram of globe types of globe valve

Gate valves also known as (knife or slide valves) are liner flow bi-directional shutoff valves that can be used to allow or disallow flow of liquid, gases and sludge through its path, the movable element in a Gate valve is a wedge-shaped disk that seats against two tapered faces in the valve body.

Gate valves are categorized according to the type or shape of it wedge disk that could be
Flexible wedge, Solid wedge, Split wedge, Parallel slide gate.

Plug valve, or cock, is a conical plug with a hole perpendicular to its axis fitting in a conical seat in the valve body at right angles to the pipe. By turning the plug the hole is either lined up with the pipe to permit flow or set at right angles to block the passage.

 Plug valves are used in verity of ways to transfer fluids to single or multiple destination by the different type of its designs.

 











Butterfly valves are circular disk valve pivoted through the radius of a diameter on the valve. The disk plate is often made of stainless still, in the fully open position the disk is opened such that it is parallel to the flow in the Pipeline and fluid flows at full, butterfly valve can be used to throttle the flow of fluid.





There are various types of butterfly valves.

1. Concentric butterfly valves are valves with resilient rubber seat with a metal base. 
2. Double-eccentric butterfly valves these are high-performance butterfly valves or double-offset butterfly valves) and different type of materials is used for the seat and disc.
3.  Triple-eccentric butterfly valves are valves that have seats which are either laminated or solid metal seat design.

Check (non-return) valves, are part of valves that operates automatically; for example, are
self-acting and permit flow in one direction only. They are made of several types of metals. The movable element in the check valve is a disk that hangs and flow freely towards a direction and rest on the inner circumference of the valve and act as a seal for flow towards its direction.

Safety valves, which are usually of the poppet type,they are usually of the pneumatic type that open at a predetermined pressure. The movable element may be kept on its seat by a weighted lever or a spring strong enough to hold the valve closed until the pressure is reached at which safe operation requires opening or the movable element moves when it is required to activate a plunger.

On gasoline engines, poppet valves are used to control the admission and rejection of the fuel intake into and out of the engine, the valve consists of a disk with tapered edge attached to a shank that is held against a tapered seat by compressed spring. The valve is raised from its seat by the action of a rotating cam that pushes through the bottom of the shank, permitting gas flow between the region, which leads to the intake or exhaust pipes, and region, which leads to or out of the cylinder of the engine.

Spool valves, In hydro-static fluid-power systems, in which the working medium is usually pressurized oil, spool valves are employed to regulate the oil flow. The valve provides two flow paths for the output from a pump through the valve which are the inward and outward position as it relates to the use of your car clutch and braking systems. Spool valves are valves that can be used as positioning valves in hydraulic systems.

 Ball Valve, these are liner vale that works as a unidirectional flow valve from the quarter-turn valve

family it works with a circular perforated ball that pivots with the use a lever on the top, when the lever is turned to a quarter, the circular ball turns such that the perforated portion of the ball is turned towards the flow of fluid, such that it flows through the perforated hole. This type of valves are easy to control and very durable and close securely after many cycles of opening and closing but they are not good at throttling.






 

      
 

References: google site for pictures
Britannica Encyclopaedia
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Agunbiade Nurudeen Adeola
Updated 11/08/2016