Bleeding your liquid device tutorial
Alicat differential pressure based liquid flow meters and controllers should only be used to flow liquids. Sometimes, however, a liquid contains trapped air or gas bubbles. It is critical that the device only measures the pressure of the gas-free liquid flowing through the device (no bubbles), or readings will be incorrect.
Each liquid device is equipped with two bleed ports on the front, used to remove any trapped air or gas in the pockets near the sensor ports. Bleeding a port is the process of loosening the nylon screw slightly so the flowing liquid leaks and allows bubbles to escape.
Below are instructions on how to properly use the bleed ports on an Alicat device. Before you begin, ensure that the meter/controller installation is secure, and add line pressure to the system. It is a good idea to have a towel handy to soak up any dripping liquid.
- For controllers, give the device >50% setpoint. For meters, make sure line pressure is applied.
- Loosen the upstream bleed port (if the device is mounted horizontally and facing towards you, this will be on the left-hand side) by turning the screw 1-2 turns slowly. If you loosen the screw too quickly, you can get a stream of water rush out of the device that can spray in unpredictable directions.
- Tap the flow body of the device gently to add some manual force in removing any bubbles.
- Allow the water to drip for about 15 seconds.
- Tighten the screw until the bleeding stops. Be careful to avoid over-tightening the screw, which can damage the tip of the nylon screw.
- Repeat these steps with the second bleed port.