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Three way control valve

Three way control valve

Three way control valve

Hi All
I'm designing a tempered oil system to run through the jacket of the tank to control the process fluid temperature inside the tank. The tempered oil system has an oil cooler, cooled by glycol. There is a three way at the inlet of the glycol cooler to bypass the cooler, when needed to give a blended temperature. When the system calls for heating the three way valve will bypass more oil around the cooler, when the system calls for cooling, it will divert more flow through the cooler. Another way of doing this is, install a control valve on the glycol line to control the hot oil temperature. Using a two way glycol control valve is much more cheaper than using a hot oil three way valve. It reduces piping, insulation etc..
Your thoughts are much appreciated

RE: Three way control valve

There are many complexities to consider in such a system. What is your source of heat? The way you describe the system heat is only coming from your tank, so it is a cooling only system, not heat/cool. If you are providing any heat, the cooling loop must be completely closed during heating.

You need to consider thermal shock to the tank and piping when going from heating to cooling. If you throttle the glycol you have to consider the possibility of boiling the glycol in the heat exchanger and the fact that the glycol in the heat exchanger may have significant heat capacity that will continue to absorb heat, and perhaps boil, after the glycol flow is stopped. Ultimately, most systems like yours use simple throttling valves or solenoid valves for control, rather than 3-way valves. If you want more detailed advice, provide a process flow diagram with the relevant temperature ranges.

RE: Three way control valve

A regular control valve is more reliable than 3way control valves. However, check that you have a min flow control loop (or a max dP loop, whichever is appropriate) for the protection of the glycol coolant recirculation pump when you make this change at the tempered oil - glycol cooler HX.

RE: Three way control valve

A lot depends on the temperature of the oil and how tight a temperature control you need.

With a double indirect system like this there will be a time lag between sensing the internal tank contents temperature and the temperature of the oil.

If the oil temp is high then you might need to allow a small flow through the cooler of glycol at all times to prevent boiling.

Also depends on where the heat is coming from - the tank contents or an external source?

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