piston pump-temp problem

[zesaint007]

Hello,

I have here a problem that i could never imagine of hapening and with these instruments already installed in the field...I bought around a Wob-L Piston Vacuum Pump (Rietschle Thomas) Snr:80061068 (12VDC) and i have a very specific question regarding the operations conditions of this kind of pump. I would like to know if there is a minimum flow rate required in order to limit the temperature rise (and if yes how much is it). Today after using it for 3 hours, the Teflon tubings used for the fittings just melted... and a collegue burnt his finger... So the temperature must have rised to more than 150 oC (The pump was in a paperboard box without any ventilation). The vacuum (controled by a needle valve) at the input was at around 19inHg for an input flow rate of 1.5lpm (conditions given by the flow cruve).

I really apreciate any kind of advice for this problem.

 

[MintJulep]

have a very specific question regarding the operations conditions of this kind of pump. I would like to know if there is a minimum flow rate required in order to limit the temperature rise (and if yes how much is it).

Why ask us? The manufacturer probably has this information.

The pump was in a paperboard box without any ventilation

Where exactly did you expect the heat generated was going to go?

 

[zesaint007]

thx for your answer
i asked you this question cause i ve found some equations (to find minimum a flow rate required in order to limit the temperature rise) but the don t seem to work very well....

 

[MintJulep]

The density of air at decreases as vacuum increases.

That is to say, the heat capacity of a vacuum is really small.

Maybe that's why it is used inside Dewar flasks.

 

[MikeHalloran]

You'd overheat in a paperboard box with no ventilation, too.



Mike Halloran
Pembroke Pines, FL, USA

 

[zesaint007]

thank you guys
in fact, the only answer that the manufacturer was abable to give me is that a need to provide a cooling for my pump...
That said do you know if the folowing equation (minimum flow rate to protect my pump from heating problems) is suitable for my case:
Qmin=P(@minflow in KW)*3600/Cp * Rho (density@Tmin)* Delta T (max temperature variation to protect my equipment)

 

[zekeman]

That formula is incorrect and is meaningless in the context in which you are using it. If you want to cool this thing, you can't use the low density air to do it. You must blow air over the unit externally and do a thermal analysis including heat transfer.
The actual formula is:
P=Q*Rho*cp*delta T

 

[zesaint007]

thanks a lot