Karnish Instruments Airplane suction gauge * Part Number: AC-158 * Units: Inches Click here to purchase or contact the seller of this item on eBay
Current Price: 28.00 USD

Suction Gauge

The gauge in the image is a suction indicator(specifically part number AC-158) manufactured by Karnish Instruments. 

It is a common aviation instrument used to monitor the performance of an aircraft's vacuum system, which powers gyroscopic flight instruments like the attitude indicator and heading indicator. 

Instrument Details

• Manufacturer: Karnish Instruments
• Part Number: AC-158
• Units: Inches of Mercury (inHg)
• Range: 0 to 10 inHg 

• What it Measures

The gauge displays the differential pressurebetween the ambient atmosphere and the vacuum system lines. 

Aviation Stack Exchange

• Normal Operation: For most general aviation aircraft, like a Cessna 172, the desired suction reading is typically between 4.5 and 5.5 inHg.
• 0 Reading: This indicates atmospheric pressure, meaning the vacuum pump has failed or the system is not running.
• High Reading: A reading significantly above the normal range (approaching 10) can indicate a system clog or a faulty regulator.