Solenoid Valves, fluid through Nozzle - not closing

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mjl1982
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Hello

I have a problem that I can't understand...

I am putting kerosene pressurised to 160psi through a 1/4" BSP solenoid with 13mm orifice.

On the out port of the solenoid is a 1/4" BSP to 2mm ID nozzle.

The idea is it sprays out a stream of kerosene.

The kerosene is provided by a pressure vessel that is charged with nitrogen. The outlet going to the solenoid is at the bottom, the inlet from the N2 is at the top.

This works fine, except the first time it is used after charging the vessel with fuel and N2 gas. In this situation there is N2/air in the line between the vessel and the solenoid input. On pressurising and opening the solenoid valve first gas comes out, then fuel. The fuel fires out and won't turn off. It takes a random time up to a few seconds to stop after removing power to the coil.

Energising the coil immediately afterwards results in normal operation.

I can then repeat the problem by turning the vessel upside down and clearing the solenoid line of fuel. Reverting the vessel to the correct orientation and opening the solenoid again results in the same problem as above.

Does anyone have any idea what is going on! I can't see how it's failing on the first opening.

The solenoids are pilot style... so I wonder if the air coming through is causing problems pushing down on the plunger?

Thanks

Mat
 
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Pilot operated SV's have a chamber that will be filled with air until they're operated or flushed out with the liquid. Sounds like that's what's happening. The air has to be flushed out of that chamber first.
 
Thanks for the quick reply.

Why doesn't the air work like the liquid does? Is it because it compresses?

Also can you recommend a type of solenoid valve that would work? I believe pilot operated is most common for the dimensions and pressures I'm working with.

Thanks

Mat
 
mjl1982 said:
Why doesn't the air work like the liquid does? Is it because it compresses?
That's probably what's going on. Why not just keep it filled with liquid? Does it get air in it under normal circumstances?

If it doesn't work for you, you can go with a direct acting SV or contact the mfg for recommendations.