Description
Overview
The ControlAir Super Mite 71L/71H Air Relay is a compact pneumatic high- or low-pressure selector designed to compare two input signals and automatically pass the selected signal downstream while blocking the other. The Mite 71H selects the higher of two pressures, while the Mite 71L selects the lower.
Its snap-acting design provides almost instantaneous signal selection and can distinguish pressure differences as small as 0.1 psi. Although ordered as either a high-pass or low-pass relay, the unit can be converted in the field from one function to the other, providing flexibility for changing process requirements.
The Super Mite 71L/71H is well suited for valve control, pneumatic pressure limiting, signal selection, and fail-safe process applications. Its passive pneumatic design requires no electrical power and supports reliable operation in petroleum, chemical, gas-field, pharmaceutical, and other industrial systems.
Key Features
- Automatic high- or low-pressure selection
- Mite 71H passes the higher of two input signals
- Mite 71L passes the lower of two input signals
- Blocks the unselected pneumatic input
- Almost instantaneous signal selection
- Can distinguish pressure differences as low as 0.1 psi
- Field-convertible between high-pass and low-pass operation
- Compact design for high-density pneumatic systems
- Passive pneumatic operation requires no electrical power
- Suitable for air or compatible gas service
- Can open or close valves when signal pressure crosses a selected condition
- Can prevent valve travel beyond a critical pressure limit
- Rugged industrial construction
- Broad operating temperature range
- Designed for process-control and safety applications
Performance Characteristics
- Relay Function: High-pressure or low-pressure pneumatic selection
- Number of Inputs: Two
- Selection Differential: As low as 0.1 psi
- Maximum Pressure Rating: 100 psig
- 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: 3.375″ diameter × 2.5″
- Materials: Aluminum, plated steel, neoprene, brass, and stainless steel
- Operating Medium: Air or compatible gas
- Switching Action: Automatic and snap-acting
- Field Conversion: High-pass to low-pass or low-pass to high-pass
In a Mite 71H configuration, the relay compares the two pneumatic inputs and passes the higher pressure to the outlet while blocking the lower signal. In a Mite 71L configuration, the relay passes the lower pressure while blocking the higher signal. The internal selector shifts automatically as the relationship between the two input pressures changes.
How to Select the Right Configuration
Selecting the correct Super Mite 71 configuration depends on whether the application must pass the higher or lower signal and how the selected output will be used in the pneumatic control system.
- Select the Mite 71H when the higher of two pneumatic signals must be passed downstream.
- Select the Mite 71L when the lower of two pneumatic signals must be passed downstream.
- Use a high-selector arrangement for override control where the strongest signal must take priority.
- Use a low-selector arrangement for limiting, shutdown, or protective control where the weakest signal must take priority.
- Use paired Mite 71H and 71L relays to create upper and lower pneumatic pressure limits.
- Confirm that both input pressures remain below the 100 psig maximum rating.
- Verify that the selected signal direction matches the desired valve action.
- Consider field conversion when process requirements may change between high- and low-selector operation.
For additional guidance:
Applications
The Super Mite 71L/71H is used in pneumatic systems that require automatic selection between two pressure signals.
- High-pressure signal selection
- Low-pressure signal selection
- Pneumatic override control
- Valve opening and closing control
- High- and low-pressure limiting
- Double pneumatic stop systems
- Safety shutdown systems
- Process interlocks
- Backup signal selection
- Oil and gas process controls
- Chemical processing systems
- Gas-field controls
- Pharmaceutical process equipment
- OEM pneumatic logic systems
Explore more applications:
Models & Configurations
Standard Models
- Mite 71H = High-pressure selector that passes the higher of two input signals
- Mite 71L = Low-pressure selector that passes the lower of two input signals
Field Conversion
- The Mite 71H can be converted in the field to low-pass operation.
- The Mite 71L can be converted in the field to high-pass operation.
Pressure Selection Codes
- Hi = Higher of two pneumatic pressures
- Lo = Lower of two pneumatic pressures
Use the ordering diagram in the current Mite Series specification sheet or contact ControlAir to confirm the complete ordering code for the required selector configuration.
Technical Resources
FAQs
What does the Super Mite 71L/71H air relay do?
The relay compares two pneumatic input pressures and automatically passes either the higher or lower signal downstream while blocking the other.
What is the difference between the Mite 71H and Mite 71L?
The Mite 71H passes the higher of two input pressures. The Mite 71L passes the lower of the two pressures.
How quickly does the relay select between signals?
The snap-acting design provides almost instantaneous signal selection.
What is the smallest pressure difference it can detect?
The Mite 71 can separate pressure differentials as small as approximately 0.1 psi.
Can a Mite 71H be converted to a Mite 71L?
Yes. The relay can be converted in the field between high-pass and low-pass operation.
What is the maximum pressure rating?
The maximum pressure rating is 100 psig.
What port size does the relay 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 71 require electrical power?
No. It is a passive, fully pneumatic selector relay.
Can the relay be used to control a valve?
Yes. It can open, close, or limit valve movement based on which pneumatic signal is selected.
Can two Mite 71 relays establish high and low limits?
Yes. A Mite 71H and Mite 71L can be combined to create upper and lower pneumatic pressure limits within a control-signal range.
