Air control relay valves are often an integral part of an air starting system. While there are many different types, sizes and manufacturers of relay valves, their basic common functions are virtually all the same. Popular manufacturers of air starting valves include companies like Ingersoll Rand, TDI, and Sealco. Relay valves provide immediate response to ensure air starter to flywheel engagement and disengagement. This helps prevent damage to the starter pinion and the flywheel ring gear. When damage to either of these parts appears, a faulty relay should be suspected and checked for proper function.
Relay valve construction and operation are fairly simple. Most relay valves consist of an aluminum body with main ports for supply air and control APP ports. Inside the valve, a spring-loaded piston sealed with Viton or Buna rubber travels up and down the bore of the valve. When either an electrical signal is sent to a solenoid, or manual control air is sent to the application port, the main air supply ports are opened to allow full air volume to flow through the valve and on to the air starter. When the operator releases the start switch or control air button, relieving the air pressure, the return spring will depress and shut off the main air flow.
Modern air starter systems typically use a so-called pre-engagement mechanism, meaning that the starter’s drive gear moves into a meshed position with the teeth of the engine flywheel before (pre-engaged) the starter motor begins to rotate. This action ensures a smooth and positive meshing of gear and prevents gear damage. A relay valve is essential to a pre-engaged system. The relay valve’s control ports send signal air pressure to a sealed piston cup located behind the drive gear. This air pressure pushes the drive gear into position on the flywheel. Once in the correct position, the signal air is released through a second control port and back to the relay valve. That signal air pressure depresses the valve piston and opens the main air supply. When the start button or control air is released, the return spring closes the main port and retracts the drive pinion away from the flywheel. Applications using a direct inertia engaged drive pinion may still require a relay valve. In these cases, the control ports of the valve are sealed and a push to start button with or without an electrical solenoid will send signal air directly to the valve, thus opening the main supply line.
Relay Valve – Air Starting Tip
Operators should position the relay valve as close as possible to the starter and reduce the number of piping elbows. Limiting the length of control air lines leading from the valve to the control ports of the starter will also improve performance by reducing pressure drops.
Air, Natural Gas and Nitrogen
While air starting relay valves all are designed to operate with air pressure, some are designated as safe to use with natural gas or nitrogen. Natural gas is sometimes used out of necessity because a reliable volume of compressed air is not available in remote locations. Natural gas pipeline compressors will often use the compressed pipeline gas instead of air to start the engine.
Air Starter Relay Valve Piping
Many valves on the market can be used as a starting air valve or a pilot operated relay control valve. They are designed to be piped according to accepted ASME piping practices as well as bolted in place for added protection against vibration and wear. Always located the relay valve as close as possible to the starter.
Relay Valve Maintenance
Equipment operators should periodically inspect relay valves for any thread wear, damage from accidental impact or internal damage caused by poor air supply quality, water or gaseous fluids and chemicals. Most manufacturers offer relay valve repair kits that consist of new parts, O-rings, seals and lubricants. Caution should be used when opening a relay valve as residual pressure may exist. Make certain residual pressure is relieved before dismantling any valve.
Relay Valve Pipe Sizes
- 1.00 inch
- 1.25 inch
- 1.50 inch
- 2.0 inch
Control Port Size
- 0.25 inch
Relay Valve Construction Material
Most modern relay valves are made using high tensile strength aluminum or stainless steel. Nickel plating and anodized parts are often used as well to help prevent corrosion and prolong life of the valve.
Relay Valve Cost
Prices range from $200 to $2000 depending on type and features. Cost is determined by valve features such as an integrated electrical solenoid, or materials like explosion proof stainless steel.
Operating Pressures
Most manufacturers publish a maximum safe operating pressure not to exceed 150 psig (10.3 BAR). Actual burst pressure is higher, and users should consult with the individual manufacturer. Users should never exceed the published safe operating pressure on any relay valve.
How to Purchase Relay Valves
You can contact MASCO for more information about relay valves. MASCO stocks and sells the following makes and models.
- Ingersoll Rand: SRV100, SRV125, SRV150, SRV150SS, SRV150-TK3 kit
- TDI: RLVA-25683-001-2-01
- Sealco:10900, 6900, 11900, 109-5 kit.