Start-up precedure of sliding vane pumps?

[heinasirkka]

Dear forum users,

We have a sliding vane pump installed as inline in a closed-loop power cycle working with a refrigerant. The pump serves for overcoming the pressure drop (1-2 bar). The problem is, the pump cannot deliver any flow. When we are buying from the company, we gave the refrigerant info (viscosity), desired flow rates, pressure drop and other relevant info and they offered this pump. Thus, I suppose the pump normally should be able to work.

There is a liquid receiver (with a subcooler at its outlet) before the pump. Even though we run the subcooler completely, there is immediate cavitation and no flow at all. The subcooler is calculated to overcome the cavitation risk, but the cavitation happens since there is no flow at all. The initial pressure in the cycle is slightly in vacuum at "before start-up" conditions. Eventually we will work at 8-10 bars.

To add, all the valves are open, so there is no blockage in the cycle for the flow. The tubing of the cycle has 10.9 mm ID.

I think we are doing something wrong when starting up the pump. To test, we pressurized the system beforehand by heating up without flow (it is not recommended), but the result was the same. I'd be very thankful if you could share and advice or experience about this.

Kind regards,
heinasirkka

 

[hydtools]

Perhaps you are not running the pump at high enough rpm to cause the vanes to slide out to contact and seal against the outer ring.

Ted

 

[heinasirkka]

Hey Ted, thanks for the reply. I also tried directly starting with high rpm. It still has cavitation.

As extra information, we did two leaks tests, one under vacuum and one under pressure. So there should be nothing going in or out of the cycle.

 

[LittleInch]

Can you draw this out schematically and add pressures , flows, temperatures and vapour pressure at relevant points.

Also pump details.

From the limited information available it sounds like you're creating a vacuum as soon as you're starting the pump or that the pump is too big.

Have you tried starting at lowest possible RPM ( is this a VFD pump?)
Have you followed the vendor recommendations for first fill and stsart-up?

You have only supplied minimal information and more times than not the issue is not a pump problem but a system problem.

Does the pump get very cold? What are the rotors made of? Could there be any water left in it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.