About the authorHand Expansion Valves – 3
In this entry a unique application for hand expansion valves (HEV) is discussed. Many vessels in industrial refrigeration systems have what we call “float columns”. These float columns usually have mechanical float switches which actuate on predetermined liquid levels within the vessel. It is also common to find capacitance type level probes installed in the float columns to monitor liquid level in the attached vessel.
A float column will have two connections on the associated vessel (top and bottom). The lower float column connection allows liquid from the vessel to reach an equilibrium level with the liquid level in the vessel. The upper connection is for equalizing pressures and gas formation in the float column with the pressure in the associated vessel.
As you may have noticed, the liquid level in a float column will fluctuate during operation. This may be the result of pressure changes in the system, which result in boiling of liquid within the float column. This can cause the apparent liquid level to change much like the level of water appears to increase in a pan of boiling water.
One method of minimizing the variation in the liquid level in the float column is to use a hand expansion valve in the top equalizing connection from the float column to the vessel. By using the HEV to partially restrict the gas flow through this top equalizing line you limit the pressure changes within the float column. Thus, by mitigating the pressure fluctuations within the float column the boiling action is minimized and results in a stable liquid level. This may help to reduce nuisance actuation of float switches.
Tags: facility operations, float columns, hand expansion valves, operating issues, System design
