Description
Overview
The ControlAir Super Mite 74 Air Relay combines the snap-acting control functions of the Mite 70 with a precision 2-way or 3-way pneumatic valve in one compact package. It is designed to channel air automatically in response to an increasing, decreasing, or remote pneumatic signal.
When the selected trip condition is reached, the internal valve changes state to open, close, lock, or vent the connected pneumatic circuit. The Mite 74 remains in the tripped condition until the proper control signal is restored and the reset button is pressed, providing dependable latching action for shutdown, alarm, and process-interlock systems.
The Super Mite 74 can also be combined with Mite 71 high- or low-pressure selectors so it trips when either of two monitored signals rises above or falls below a selected pressure. Its fully pneumatic design requires no electrical power and is suitable for air or compatible gas service in demanding industrial applications.
Key Features
- Snap-acting pneumatic control relay
- Integral precision 2-way or 3-way valve
- Responds to increasing, decreasing, or remote pneumatic signals
- Provides trip-to-open or trip-to-close valve action
- Can lock or vent output pressure when tripped
- Manual reset maintains the tripped condition until intentionally restored
- Compatible with Mite 71 high- and low-pressure selectors
- Can respond to either of two pneumatic input signals
- Crisp and repeatable switching action
- Compact design for high-density installations
- Passive pneumatic operation requires no electrical power
- Suitable for air or compatible gas service
- 100 psig maximum pressure rating
- Broad operating temperature range
- Rugged aluminum construction
- Designed for safety, shutdown, alarm, and process-control systems
Performance Characteristics
- Relay Function: Snap-acting pneumatic control relay with integral valve
- Valve Configurations: 2-way or 3-way
- Trip Inputs: Increasing signal, decreasing signal, or remote pneumatic signal
- Maximum Pressure Rating: 100 psig (7 bar)
- Operating Temperature Range: -40°F to 180°F (-40°C to 82°C)
- Port Connections: Tapped for 1/4″ NPT with 1/8″ internal ports
- Approximate Dimensions: 2.5″ diameter × 5″ high
- Approximate Weight: 2 lb (0.91 kg)
- Body Material: Aluminum
- Other Materials: Plated steel, neoprene, brass, and stainless steel
- Reset Method: Manual push-button reset
- Operating Medium: Air or compatible gas
- Output Functions: Trip to open, trip to close, lock, or vent depending on valve configuration
During normal operation, the variable instrument-air signal is monitored at the control port. When the signal reaches the selected trip condition, the snap-acting mechanism shifts the integral valve. In a 2-way configuration, the common outlet can be locked when tripped. In a 3-way configuration, the common outlet can be vented through the exhaust port. The relay remains latched until the control signal returns to normal and the reset button is pressed.
How to Select the Right Configuration
Selecting the correct Super Mite 74 configuration depends on valve function, supply-pressure range, monitored signal range, reset-button arrangement, and required trip action.
- Select a 2-way valve configuration when the common outlet must lock pressure when the relay trips.
- Select a 3-way valve configuration when the common outlet must vent when the relay trips.
- Select trip-to-open action when the valve must open after the monitored condition reaches the trip point.
- Select trip-to-close action when the valve must close after the monitored condition reaches the trip point.
- Select an increasing-signal configuration when the relay must trip as pressure rises.
- Select a decreasing-signal configuration when the relay must trip as pressure falls.
- Select the high-signal configuration for monitored signal pressures above 50 psig.
- Select the low-signal configuration for monitored signal pressures below 50 psig.
- Select the high-supply configuration for supply pressures above 50 psig.
- Select the low-supply configuration for supply pressures below 50 psig.
- Select the standard reset button for typical installations.
- Select the long reset button when extended reach or panel accessibility is required.
- Use a Mite 71 selector when the Mite 74 must respond to the higher or lower of two signals.
- Confirm that system pressure does not exceed the 100 psig maximum rating.
For additional guidance:
Applications
The Super Mite 74 is used in pneumatic systems that require automatic valve switching, pressure lock-up, venting, shutdown, or process interlocking based on a monitored signal.
- On-off pneumatic valve control
- Emergency shutdown systems
- High-pressure and low-pressure trips
- Valve lock-up systems
- Valve venting systems
- Pneumatic process interlocks
- Remote pneumatic trip systems
- Alarm and safety circuits
- Oil and gas process controls
- Petroleum processing systems
- Chemical processing equipment
- Gas-field safety systems
- Pharmaceutical process controls
- OEM pneumatic logic systems
Explore more applications:
Models & Configurations
Base Model
- Mite 74 = Snap-acting pneumatic control relay with integral 2-way or 3-way valve
Valve Configurations
- 2-Way Valve = Common outlet locks pressure when tripped
- 3-Way Valve = Common outlet vents through the exhaust port when tripped
Supply Configurations
- High Supply = Supply pressure above 50 psig
- Low Supply = Supply pressure below 50 psig
Signal Configurations
- High Signal = Monitored signal above 50 psig
- Low Signal = Monitored signal below 50 psig
Reset Button Configurations
- Standard Reset Button = Normal reset-stem length
- Long Reset Button = Extended reset stem for panel or recessed installations
Pneumatic Connections
- A = Variable instrument-air signal
- B = Signal output that locks pressure when tripped
- C = Signal output that vents when tripped
- D = Remote pneumatic trip
- G = Trip-to-open port
- H = Common outlet
- I = Trip-to-close port
Use the ordering diagram in the current Mite Series specification sheet or contact ControlAir to confirm the complete ordering code for the required valve, supply, signal, and reset configuration.
Technical Resources
FAQs
What does the Super Mite 74 air relay do?
The Super Mite 74 combines a snap-acting pneumatic control relay with an integral 2-way or 3-way valve to open, close, lock, or vent a pneumatic circuit when a trip condition is reached.
What is the difference between the 2-way and 3-way versions?
The 2-way version can lock pressure at the common outlet when tripped. The 3-way version can vent the common outlet through the exhaust port.
Can the Mite 74 trip on rising or falling pressure?
Yes. It can be configured to trip on either an increasing or decreasing pneumatic signal.
Can the relay be tripped remotely?
Yes. A separate pneumatic connection allows the Mite 74 to be tripped from a remote signal.
What happens after the relay trips?
The Mite 74 remains in the tripped condition until the control signal is restored and the reset button is pressed.
Can the Mite 74 monitor two signals?
Yes. It can be combined with a Mite 71H or Mite 71L selector so it responds to the higher or lower of two pneumatic signals.
What is the maximum pressure rating?
The maximum pressure rating is 100 psig (7 bar).
What port size does the Mite 74 use?
The relay is tapped for 1/4″ NPT connections with 1/8″ internal ports.
What is the operating temperature range?
The operating temperature range is -40°F to 180°F (-40°C to 82°C).
Does the Super Mite 74 require electrical power?
No. It is a passive, fully pneumatic relay and valve assembly.
What are common Mite 74 applications?
Common uses include on-off valve control, emergency shutdown, high- and low-pressure trips, valve lock-up, venting, alarms, and pneumatic process interlocks.
