Hand Expansion Valves - 4

In the final entry on this series, the application of hand expansion valves (HEV) to liquid overfeed systems will be discussed.  The application of HEV’s in this type of system somewhat differs from those of the prior discussions.  When selecting HEV’s for the evaporators where liquid overfeed is being utilized the hand expansion valves take on a secondary function, which may not be obvious at first glance.

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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.

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We have been somewhat busy the last few weeks completing a new project.  The next few blog entries should be more timely.

These valves are used for multiple purposes in ammonia refrigeration systems.  However, they are commonly designated by a single description.  This common term of hand expansion valve (HEV) is sometimes misleading. It may help to consider the actual function the valve provides; throttling of liquid or vapor and the mass flow requirements for the application.

The common applications of this valve are:

• Liquid make-up to maintain a relatively constant liquid level in a vessel.
• Throttling liquid from a higher pressure to a lower pressure (control pressure systems).
• Balancing upstream liquid pressures to evaporators in a liquid overfeed system.
• Throttling vapor flow in float columns to minimize rapid liquid level fluctuations.

The next few blog entries will discuss the multiple applications of these valves.

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