Valves 101: Types of Ball Valves
d11ing11p > 11-11-2021, 05:35 AM
Valves 101: Types of Ball Valves
Ball valves are a type of piping equipment that shuts off or controls the flow in a pipeline by using a hollow sphere and round seats held in a valve body. There are two basic technologies for the design of ball valves, floating ball design and trunnion mounted ball design.
The major components of a ball valve include:
Valve body – A pressure vessel that contains the components needed to control or shut off the flow through a pipe. It is designed to connect two or more sections of pipe or tubing to each other.
Ball – A sphere with a flow path (hole or tunnel) through the center of it and a connection point for a shaft to rotate it.
Seats – Round donut-shaped discs that form a seal between the body and ball.
Stem – A shaft that connects the internal ball to the outside of the valve to facilitate rotation of the ball.
Packing – Flexible seals that fit around the shaft and prevent the media traveling through the valve from escaping externally.
Bonnet – The part of the valve body that houses the stem and packing.
Operator or Actuator – An external device designed to rotate the stem of the valve. This can be a lever, a gear, a motor-operated gear (electric actuator), or a pneumatic/hydraulic actuator.
Floating Ball Design
A floating ball valve sandwiches the hollow ball between two or more cupped seats that form a tight seal between the body and the ball at the inlet and outlet ports of the valve body.
The ball is rotated (usually 90 degrees) by a shaft that protrudes outside of the valve body and is connected to some form of operator. For this reason, most ball valves are referred to as quarter-turn valves. This shaft is not rigidly attached to the ball in order for the ball to pivot on the end of the shaft as it rotates on the axis of the ball. This is usually accomplished with a slot on top of the ball, perpendicular to the ball’s flow path. The cupped portion of the seats cradle the ball prevents it from moving down in the valve body.
The valve packing prevents the media from escaping the valve body through the stem opening in the bonnet. The most common type of packing today is chevron v-ring type packing. If you look at the cross section profile of this packing, it resembles the letter “V”. The outer diameter of the packing matches the bore of the bonnet. The inside diameter matches the outer diameter of the stem. Multiple rings of this packing are stacked on top of each other and the stem is inserted through the packing. A packing gland on top of the bonnet pushes down on the top of the “V” and causes the packing to expand and seals agains the stem and bonnet.
Trunnion Mounted Ball Design
The trunnion design ball valve works nearly the same way as the floating ball except the seats are spring loaded against the ball and the ball does not pivot. The ball only rotates on its axis in this design.
In the trunnion mounted ball valve, the ball utilizes a second shaft and bearing on the bottom of the ball. This stem or “post” holds the bottom of the valve in place. The top of the ball is not slotted and the upper stem is rigidly attached to the ball. This prevents the ball from moving into the downstream seat.
Since the ball does not move into the seats, the seats must move towards the ball. Springs behind the seat push them tightly into the ball in order to make the seal.
Trunnion valves are very effective at sealing off very low pressures that would not be strong enough to move a floating ball into the downstream seat. They are also required on large diameter valves and high-pressure valves. The reason for this is the contact area of the seats in a floating ball is relatively small. From physics, we know force = Pressure x Area. The force on the downstream seat in a floating ball is derived from the process pressure in the upstream pipe pushing on the solid area of the ball in the closed position. If the pressure is high or the area is large, the downstream seat will be destroyed.
The tradeoff is that trunnion valves are much more expensive than floating ball designs.
Both floating ball and trunnion designs are available as multi-port valves by using elaborate flow paths in the ball and additional ports in the body.
Are you looking for ball valves for your facility? Our team has years of experience in selecting the perfect valve for any application. Contact us today to discuss your specific valve needs!
How It Works: Gate Valves
All valves are designed to stop, allow, or throttle the flow of a process fluid. Gate valves—one of the original valve designs—are ideally suited for on-off, primarily liquid, service. A gate valve functions by lifting a rectangular or circular gate out of the path of the fluid. When the valve is fully open, gate valves are full bore, meaning there is nothing to obstruct the flow because the gate and pipeline diameter have the same opening. This bore diameter also determines the valve size. An advantage of this fullbore design is very low friction loss, which saves energy and reduces total cost of ownership.
Gate and segment
There are four primary designs for gate valves.
Slab gate valves comprise a single gate unit that raises and lowers between two seat rings and are primarily used for transporting crude oil and NGLs. The G4N fabricated gate valve in the GROVE valves portfolio and the WKM Saf-T-Seal slab gate valve are ideal choices for this application.
Expanding gate valves include two units—a gate and segment—in contrast with slab gate valves, which have one unit. The gate and segment units collapse against each other for travel and separate when the valve is fully opened or fully closed to affect a mechanical seal.
Wedge gate valves are engineered with a tapered gate with metal-to-metal sealing. In contrast with a slab or expanding gate valve, wedge gate valves are not piggable because of the void that is left in the bottom of the valve body when the valve is open. These valves do not have a bore through the gate itself; instead, the gate retracts into the valve body when open, which saves height space.
Knife gate valves are used to cut through extremely thick fluids and dry bulk solids. The design of this valve makes it inherently self cleaning because the knife is cleared of abrasives with each stroke as it passes the seat rings and skirts. The gate unit of this type of valve is thin compared with other gate valve types and is guided in place by the water-type body that sandwiches the gate.
Gate valves can have a rising or nonrising stem design. Rising stems are attached directly to the gate and provide a visual indicator of the valve position. Nonrising stems are generally threaded into the upper part of the gate and have a pointer threaded onto the top to indicate position. Nonrising stem designs are ideally suited for applications where vertical space is limited, in well applications, and where scraping or pigging is not required.
Gate valves are designed with a sealing unit to provide a tight seal around the stem. Our patented single loaded-spring (SLS) stem seal design, used in Saf-T-Seal slab gate valves and WKM Pow-R-Seal double expanding gate valves, provides superior leak protection and a self-adjusting seal designed to reduce maintenance.
Cast Steel Flanged Gate Valve
Cast Steel Flanged Gate Valve
Suitable to fit between PN16, ANSI 150 or ANSI 300 flanges
Designed for industrial applications
Cast Steel body with bolted bonnet
End connection: Flanged PN16, ANSI 150 or ANSI 300
Sizes 2" to 8" and 2" to 10"
Temperature range: -29°C to 425°C.
Pressure rating: PN20, Class 150 or Class 300
Our Cast Steel Flanged Gate Valve is suitable to fit between PN6, PN10/16 or ANSI 150 flanges (subject to configuration) and designed for industrial applications; boiler plants and rugged environments where a more durable valve is required.
A handwheel operated manual gate valve with Cast Steel body, bolted bonnet and non rising stem. Cast Steel gate valve is used as efficient shut-off valves with flow in either direction for water, saturated steam, air, gas and oil.
The Main Types of Forged Steel Gate Valves
The main role of forged steel gate valve in the pipeline is to cut off, is a very wide application of a valve, the general diameter DN ≤ 50 cut off the device selected this forged steel gate valve. When the valve is fully open, the sealing surface eroded by the medium is smaller than globe valve. Shape is relatively simple, casting process is better. So, what types are forged steel gate valve? According to the gate construction to classify.
Parallel forged steel gate valve, sealing surface is parallel to the vertical center line. In the parallel type of forged steel gate valve, some valves install wedge, there are also between the gate with a spring, the spring can produce preload, is conducive to the gate of the seal.
Wedge forged steel gate valve, sealing surface and the vertical center line create into a certain angle, that is, two sealing surface into a wedge-shaped forged steel gate valve. Generally, the higher the working temperature, the greater the angle, to reduce the possibility of wedging when the temperature changes.
All About Globe Valves
Globe valves are mainly used to regulate and to stop fluid flow through pipes. They differ from valves such as ball valves and gate valves in that they are specifically designed to govern fluid flow and are not limited to shut-off service. Globe valves are so named because older designs exhibited something of a globular body and could be divided into two hemispheres separated by an equator, where the flow changes direction. The actual internal element that closes against the seat is not usually spherical (as in a ball valve) but more typically flat, semi-spherical, or plug shaped. Globe valves, when opened, are more restrictive to fluid flow than gate or ball valves, resulting in higher pressure drops through them. Globe valves are available in three main body configurations, some of which are intended to reduce the pressure drop through the valve.
How It Works: Check Valves
Check valves, also known as nonreturn or one-way valves, enable fluid to flow one way in a pipeline. A clapper hangs from a hinge, clapper shaft, or pin mounted to the underside of the bonnet. This design inhibits backflow in a line.
Because of their simple design, check valves generally operate without automation or human interaction and instead rely on the flow velocity of the fluid to open and close. This means they do not have a method of outside operation like a handle or lever. The minimum upstream pressure required to operate the valve is called the cracking pressure, generally between 1 and 5 psi. Check valves are designed specifically with this number in mind.
The degree of opening on a check valve is determined by the flow rate. The higher the flow rate, the more open the valve will be until it reaches its maximum, full-open position. On many check valves, the full open position is approximately 85°.
Plug type valve
Plug valves are valves with cylindrical or conically tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that fluid can flow through the plug when the valve is open.