I have a question regarding Yarway Automatic Recycle Valves.

They all seem to say they are "flow sensing", but then seem to operate mainly on springs, while some have orifices.

can anyone succinctly answer how they sense flow, and not pressure related flow (as a set spring would do).

The meaning of "flow sensing" may have a vendor specific definition.  The available literature leaves everything up to interpretation without giving a clean definition.  The following is what I can derive from literature on a Series 9300 Yarway ARV:

Recycle flow is controlled by one or more orifices for the recycle stream.  The control assembly is a combination of something like a "lift" check and an orifice stack.  At no flow, the check is seated blocking flow to the user and the orifice stack is open to the recycle line.  At low flows, the output is to the recycle line and perhaps back to the source.  As flow increases, a point is reached where the check begins to lift, and there is flow to the user and to the recycle.  Further increase in flow will further open the check and raise the orifice stack until flow to the recycle stops.

This arrangement is flow sensing only in that the recycle flow rate is determined by the orifice(s) and in that user flow is controlled by the flow required for lift force of the check.  There is no continuous sensing of flow rate with a control function to start/stop recycle.  This device will be affected by fluid and process properties.

I've installed these before on pump discharge lines in order to maintain min. flow on the pumps due to flow changes downstream of the pump. Basically, what happens is, these valves operate like a check valve and variable opening orifice. At zero main flow the bypass orifice opens wide allowing full bypass flow to occur (min. pump flow req'd.) as main flow picks up, the bypass orifice begins to close down decreasing min req'd bypass flow as main flow picks up. The energy to operate the bypass orifice is accomplished by a mechanical linkage to the main flow/check disk. If you get a drawing, it becomes self explanatory. The reason for their invention was to reduce the energy requirements of pumps that used to use continuous bypass flow through an orifice or the associated instrumentaion installation & maintenence costs of using a motor or solenoid operated bypass valve.

One little phenomenon you need to be aware of, "any energy input into a system that is not converted to work will be converted to heat" these thing make great tea kettles if you're not careful and an excellent introduction to applied Thermo.

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