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What is Valve?

Valve is a device that comes in piping system, to manage the fluid under service.

Function of Valve:

n  To start & Stop flow.

n  To regulate the flow or pressure.

n  To allow uni directional flow - Preventing Reverse flow.

n  Safety or Relief of over pressure to prevent catastrophic damage of system components.

Classification of Valves

According to Operational Features:

v  Isolation Type - Start & Stop Flow

·    Gate Valve

·    Plug Valve

·    Ball Valve

v  Regulation Type

v  Check Type - Preventing Reverse Flow

v  Safety or Relief Type

v  Special Applications

   According to Name of it’s Design:

·    Gate Valve

·    Ball Valve

·    Plug Valve

·    Butterfly Valve

·    Globe Valve

·    Needle Valve

·    Diaphragm Valve

·    Check Valve

·    Angle Valve 

   According to Mechanical Construction:

v  STEM

·    Raising Stem

·    Non Raising Stem

v  BONNET

·    Bolted Bonnet

·    Screwed Bonnet

·    Welded Bonnet

v  GLAND BOX

·    Packing Type

·    Bellows Sealed

   According to Type of End Connection:

v  FLANGED CONNECTION       

v  SCREWED CONNECTION

v  WELDED CONNECTION

·    Socket welded

·    Butt Welded

  According to Mode of Operation:

v  HAND OPERATED

·   Hand Wheel

·   Lever

ü  Remote Hand Operated

·   Chain

·   Teleflex Cable

·   Teleflex Shaft

v  MOTOR OPERATED

v  PNEUMATIC OPERATED

v  PILOT OPERATED

v  SOLENOID OPERATED

Maintenance

FREQUENT OPERATIONAL PROBLEMS

TROUBLE SHOOTING

SALVATION

Special Service Valves

 There Are Two Special Valves:

        •   Butterfly Valves

        •   Diaphragm Valves

Butterfly Valve

Butterfly Valves are used in large ducts transporting air or gas, in steam service, and in large water pipes.

Butterfly valves are used for straight, start-stop flow. A thin disc in the body of the valve provides the on-off control,

This type of valve offers little resistance to flow and has a low pressure drop through its seat.

Because of its design, the butterfly valves is not pressure-tight.

A valve operator or manual gear reducer is often necessary to open or close these valves.

Diaphragm Valves

Diaphragm Valves are used for handling corrosive or toxic fluids. A flexible diaphragm of non-corrosive material separates the process fluid from the valve’s working parts. 

The valve stem presses the diaphragm against the valve seat to prevent fluid flow. The diaphragm valve is good for throttling and controlling flow . When it is tightly closed, the diaphragm stops all fluid flow. 

These valves are used in service for chemicals, abrasive or corrosive materials, and vacuum processes.

SAFETY VALVE

Safety valves are installed on pressure vessels, boilers etc. It is mostly used in Air, Gas, Steam systems.  It blows up continuously until the system pressure comes to normal operating pressure. The over pressure is released to the open atmosphere, a flare, or some safe place.

Relief valves are installed liquid systems. It opens instantly to relieve excessive pressure from piping and vessels.The extra pressure is released within system itself.

Relief valves are designed to protect personnel and equipment.

On a piping and instrument drawing these valves are often listed as PSVs or Pressure Safety Valves.

The two terms, relief valve and safety valve are used interchangeably.

Check valves

CHECK VALVE

Unidirectional Flow

Check valves are used in applications where reverse flow would cause dangerous conditions, damage to equipment or affect the quality of the product

Lift Check Valve

Lift Check Valves are used for irregular or pulsating flows because they do not chatter as much as swing check valves. A Foot  valve is a type of vertical-Lift check valve. Foot valves are installed at the bottom of pump suction pipe submerged in a fluid, such as a cooling tower basin. The valve allows fluid to flow upward into the pipe, but not back into the basin. Because of the possibility of debris at the bottom of a basin, foot valves usually have an intake strainer

Swing Check valve

The Horizontal Swing Check Valve is the most commonly used type of check valve.

The disc hangs almost vertically and is moved by the horizontal flow of the fluid through the valve.

Swing check valves offer the least resistance to flow, but they have a tendency to create noise and vibration when flow reversed are frequent.

This noise is called chatter.

Ball Check valve 

Ball Check valves are used in processes containing viscous fluids or fluids that may contain particulate matter in them.

One of the most common uses of ball check valves is in machine lubrication systems.

Because ball check valves operate rapidly and quietly, they are used in systems where there are frequent pressure changes and flow reversals. 

Regulation Valves

Regulating or Throttling Valves

Valves are used to control or throttle the flow of fluids.

GLOBE VALVE

Globe valves are generally used in small-diameter piping

When a globe valve is opened, the surface of the disc moves away from the valve seat

The fluid flows through the valve and changes direction as it moves up and over the valve seat.

Because globe valves are designed for through they resist fluid flow well and the disc wears evenly.

Globe valves are adjusted with very few turns compared with gate valves.

Globe valves are often used in service requiring frequent valve opening and closing

NEEDLE VALVE

Needle valves use a long narrow, pointed plug to provide precise control of flow.

Needle valves are normally used in small diameter piping. Because the diameter of the valve seat is smaller, the amount of fluid flow is reduced even when the valve is fully open.

Fluid flow is easily controlled by moving the needle point of the plug into the seat.

ANGLE VALVE

Angle Valves have the same basic design and operating characteristics as globe valves.

When installed in the piping system, they provide the 90^o turn of a piping elbow. As a result, fewer fittings and pipe joints are needed.

Valve seat Design

Isolation Valves

·         Gate Valve

·         Plug Valve

·         Ball Valve

These valves are used to Start or Stop Flow of Fluids. Functionally isolation type of valves are kept either fully opened or fully closed. Isolation valves offer minimum resistance and thereby gives very low pressure drop to flow in its fully open position.

The velocity of flow against a partially opened valve can  cause:

Ø  Vibration - This may result in damage to the valve & piping.

Ø  Hammering - This may result in instantaneous jerk on piping system.

Ø  Hydraulic turbulences – This may result in erosion of the valve Gate & Seat.

The seat is the base on which the disc of the valve fits tightly. When the seat or gate is damaged, the valve will pass even in fully closed condition.

GATE VALVE

The maximum opening of the gate valve is the same size as the inside diameter of the pipe in which it is installed. Fluid flow is straight through the valve.

Gate Valves should be kept either fully Open or fully Closed

Ø  Straight-through flow

Ø  No Direction of flow

Ø  Small pressure drop

There Are Two Types of Gate Valves

Rising Stem

In the rising stem gate valve, the stem is threaded and rises when the valve is opened. Since the stem is exposed to outside atmosphere, it should be kept clean of point, dust, and dirt.

Non-Rising Stem

In the non-rising stem type, the bottom of the stem is threaded and dose not rise when the hand wheel is rotated to open the gate valve

Fluids may corrode the threads on the Non—rising stem gate valve.

Non-Rising stem gate valves are used where there is very little space.

Valve Parts

HAND WHEEL: To keep easy the rotation of the stem

BOX NUT: The threaded end of the stem, pass through the Nut. Rotation of Nut by hand wheel causes                      the stem raising or lowering the stem.

BONNET: Part of the valve mounted on the top of the body to form a tight enclosure.

BODY: Main part of the valve directly attached to the pipe

GATE: Is the part of the valve that controls the opening

YOKE: Part of the valve to support the hand wheel and bushing

GLAND: After the packing is installed the gland compresses the packing, the gland also serves as the                    stuffing box covers

STEM: Solidly connected to the gate, the rotation of the stem raise or lowers the gate

SEAT RINGS: When the gate is lowered, the seat rings fit with the gate to stop all flow

PLUG VALVE 

Plug valves are used as open-close valves. Plug valves have wedge-shaped ports.

The flow of liquid can be started or stopped by turning the plug handle only 90 ^o.

Most plug valves must be lubricated to keep them in good operating condition and make them easy to turn.

The lubricant also makes a seal around the valve to prevent leaking.

The plug valve does not have a long bonnet or exposed threads. The plug fits the body of the valve, and either its open port or its solid faces the fluid. A quarter turn is all that is needed to change from one position to the other.

Ø  Straight-through flow

Ø  Non Directional

Ø  Small Pressure drop

Ø  Multiple-way possible depending on plug

Ø  Fast Operation 

BALL VALVE

Ball Valves are also open-close valves and operate just like plug valves.

The Ball-Shaped port has a hole through it that blocks fluid flow through the valve.

When the hole is aligned with the pipe, flow is allowed.

When the ball is turned a quarter turn, the solid side of the ball blocks fluid flow.

These valves are not normally lubricated. Two rings, made of a material such as Teflon, From the seals around the ball.

About me

   

I am being a Mechanical engineer with 40 years of experience in maintenance of production line and Power plant machines. During my services, I had come across many different kinds of problems and breakdowns which leads to partial or total shutdown of the plant. A suitable & safe method had to be adopted to fix the deficiency and put back the machine into operational. 

In my entire tenure, I had taken up many challenging tasks and successfully solved the issue. To expedite the maintenance, it is very much essential to understand the technology of machine. 

The idea of this website is to share my experience with young generation of Mechanical Engineers. 

Here is a moral story of an Old man's Experience.

A giant ship engine failed. The ship’s owners tried one expert after another, but none of them could figure but how to fix the engine.

Then they brought in an old man who had been fixing ships since he was a young. He carried a large bag of tools with him, and when he arrived, he immediately went to work. He inspected the engine very carefully, top to bottom.

Two of the ship’s owners were there, watching this man, hoping he would know what to do. After looking things over, the old man reached into his bag and pulled out a small hammer. He gently tapped something. Instantly, the engine lurched into life. He carefully put his hammer away. The engine was fixed!

A week later, the owners received a bill from the old man for ten thousand dollars.

“What?!” the owners exclaimed. “He hardly did anything!”

So they wrote the old man a note saying, “Please send us an itemized bill.

The man sent a bill that read:

Tapping with a hammer………………….. $ 2.00

Knowing where to tap…………………….. $ 9,998.00

Effort is important, but knowing where to make an effort makes all the difference!

Good Luck