A compression shut off valve is a type of valve used to control the flow of liquids or gases in plumbing or industrial piping systems. It gets its name from the way it seals when closed – the valve’s handle compresses a rubber gasket against the valve seat to create a tight seal and stop flow. Compression valves are one of the most common types of manual valves found in residential and commercial applications.
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How Does a Compression Shut Off Valve Work?
A compression valve uses the force of the valve handle to squeeze a rubber gasket against a metal seat, cutting off the flow. When the valve is open, the gasket is loosened and flow can pass through. When closing the valve, the handle threads drive a stem down into the valve body. This stem presses against the gasket, sandwiching it tightly between the stem and seat. The gasket material fills any small gaps and prevents flow from getting through when closed.
Compression valves have three main components:
- Valve body – The main cylindrical body containing the flow way, seat, and threads for the bonnet.
- Stem – A threaded stem that is raised and lowered by the handle to compress the gasket.
- Bonnet – The top portion with the handle and threads that drive the stem up and down.
As the bonnet is threaded downward by the handle, the stem pushes the gasket material against the seat, deforming it to cut off flow. When opening, the stem lifts up and takes pressure off the gasket, allowing it to expand back to an open position.
Types of Compression Valves
There are a few main types of compression valves classified by their design and end connections:
Compression Ball Valve
The ball valve design uses a spherical ball with a hole drilled through it to control flow. As the handle is turned 90 degrees, the ball rotates to align or misalign the hole with the valve ends. Like other ball valves, it achieves shutoff by the perpendicular orientation of the hole. The compression action seals the ball against the seat rings.
Compression Gate Valve
A gate valve uses a rectangular or round gate forced down against the seat. Compression gate valves wedge two gates together or press a single gate on the seat. They are mainly used in fully open or closed applications.
Compression Globe Valve
Globe valves regulate flow by raising or lowering a disk into the path of the fluid. Compression globe valves achieve tight shutoff by compressing the disk tightly against the seat using the stem and bonnet.
Compression Plug Valve
Plug valves use a cylindrical or conical plug with a bore to control flow. Compression plug valves press the plug into the seat using the stem to get a tight seal.
Compression Needle Valve
Needle valves use a needle-shaped plunger to close against a seat. Compression needle valves have a gland and bonnet that applies pressure to the plunger when closing.
Compression Stop Valve
Stop valves, also called angle valves or service valves, connect at pipe ends to shutoff flow. Compression stop valves squeeze a washer or gasket against the body outlet to seal.
Main Components
While compression valve designs vary, they share similar components that enable the compression sealing action:
Valve Body
The valve body serves as the main pressure vessel and contains the flow way where the sealing action occurs. It has threaded openings to connect the bonnet and inlet/outlet ends. Bodies are typically made of brass, bronze, cast iron, steel or plastic. An inner seat provides the surface for the gasket to seal against.
Stem
The stem is threaded to connect with the bonnet. As the bonnet drives down, the stem pushes against the gasket or closure element. Stems are often stainless steel or brass.
Bonnet
The bonnet provides the compressive force by threading down against the body. It contains the threads that drive the stem downward when closing. Bonnets can be plastic, brass or steel.
Handle
The handle attaches to the bonnet and allows user operation to drive the bonnet and stem up and down. It provides leverage for the force needed to compress the gasket. Handles are commonly made of steel or plastic.
Gasket
A flexible gasket provides the sealing interface between the stem and seat. As the stem compresses the gasket, it deforms to fill any gaps in the seat. Gaskets are typically rubber, PTFE, or other soft sealing materials.
Sizes
Compression valves are available in a wide range of standard pipe sizes. Common sizes include:
| Valve Size | Pipe Size |
|---|---|
| 1/8″ compression | 1/8″ OD tube |
| 1/4″ compression | 1/4″ OD tube |
| 3/8″ compression | 3/8″ OD tube |
| 1/2″ compression | 1/2″ pipe |
| 3/4″ compression | 3/4″ pipe |
| 1″ compression | 1″ pipe |
| 1-1/4″ compression | 1-1/4″ pipe |
| 1-1/2″ compression | 1-1/2″ pipe |
| 2″ compression | 2″ pipe |
Larger sizes are also produced. The pipe size indicates the inlet/outlet diameter the valve connects to.
Materials of Construction
Compression valves are constructed from materials that can withstand their intended pressures, temperatures and fluids. Common materials include:
- Brass – Standard material for valve bodies and bonnets due to good strength, corrosion resistance, and machinability. Some brass alloys contain lead for enhanced machining.
- Bronze – Used for bodies and stems when higher strength and corrosion resistance is needed. Grades like silicon bronze have good seawater resistance.
- Plastic – Economical choice for valves in lower pressure water and chemical services. PVC, CPVC, PP, and PVDF are common choices.
- Stainless steel – Used for higher pressure applications and when corrosion resistance is critical. Common grades are 304 and 316.
- Cast iron – Provides strength at lower cost in larger sizes. Can have anti-corrosion coatings.
The gasket material depends on the fluid being handled. Common options are PTFE, NBR rubber, and viton rubber.
Pressure and Temperature Ratings
Compression valves have pressure and temperature limits depending on materials, size and design. Typical pressure ratings range from low pressure residential applications up to 600 psi for industrial uses. Smaller valves often have lower pressure limits than larger valves. Common residential compression valves are often rated to around 150-200 psi at 70-80°F water temperature.
Maximum water temperatures depend on materials and gasket compounds, but range up to around 250°F. Some higher temperature plastic and metal valves can handle over 300°F. Check manufacturer data for specific temperature-pressure limitations.
Advantages of Compression Valves
Compression valves offer several benefits that make them a popular choice for flow control:
- Simple and easy quarter-turn operation.
- Tight shutoff when fully closed.
- Durable gasket seal resists leakage.
- Self-adjusting gasket compensates for wear.
- Compact and lightweight design.
- Low maintenance requirements.
- Variety of styles and connection choices.
- Relatively low cost compared to other shutoff valves.
Disadvantages of Compression Valves
Compression valves also have some disadvantages to consider:
- Not suitable for throttling flow control. Mainly used fully open or closed.
- Rubber gaskets can degrade over time depending on fluid.
- Limited maximum pressure and temperature.
- Potential for gasket pieces or particles to break off over time.
Typical Applications
Compression valves are used in a wide variety of residential, commercial, and industrial applications to shut off flow. Typical uses include:
- Shutoff valves for plumbing fixtures – sinks, toilets, washing machines, etc.
- Isolation valves for appliances – water heaters, dishwashers, etc.
- Water line shutoff valves.
- Irrigation system control valves.
- HVAC and hydronic heating system shutoffs.
- Low pressure steam valves.
- Chemical and compressed air lines.
- Industrial equipment isolation.
Plastic compression valves are common for residential water line applications, while more heavy-duty metal valves are used for higher pressure industrial piping systems.
Replacing Compression Valves
Over time, compression valves may need to be replaced if they start leaking or no longer fully shut off. Typical steps for replacing a compression valve include:
- Turn off upstream supply valves and release system pressure.
- Disconnect any handles or operators.
- Loosen and remove compression nut and any bonding wires.
- Unthread valve from piping.
- Clean pipe ends and apply fresh pipe joint compound.
- Install new valve hand tight plus 1-2 turns past hand tight.
- Reconnect compression nut and tighten.
- Reattach handle and operators.
- Restore upstream isolation valves to service position.
- Slowly open valve and check for leaks during start-up.
It’s a good idea to replace the pipe nipples when changing out valves to ensure a clean sealing surface. Follow manufacturer instructions for proper installation procedures.
Conclusion
Compression shut off valves are simple, reliable valves that use the force of the handle squeezing a gasket to achieve tight shutoff. Their straightforward design makes them ideal for routine on/off flow control applications across many industries. When selecting and sizing a compression valve, consider the required flow capacity, pressure rating, construction materials, and operating conditions. Follow proper installation and maintenance procedures to get the longest service life out of compression valves.