Cold trap questions

I would like to get a better quality vacuum pump, right now I am using a robinair vacumaster model 15500, rated for 5 cfm. I run that with no cold trap and I frequently change the oil. My problem is that I don’t want to spend good $ on a nice pump to run it like that with purged solvent through it. I live in a very small town, there is no dry ice, the closest dry ice sucks and it is 1.5 hours away, the closest pelletized dry ice or good hard block is 2.5 hours away. I can get dry ice delivered for a $25 delivery fee once every 3 weeks, which works perfect for inline dewaxing, but makes it hard to maintain a cold trap for 3-4 day low temp purge. What would you recommend? Is liquid nitrogen so what easily attainable, and will that last longer?

I like the cold trap idea, but they sure look expensive.
Liquid N is a whole different safety level from dry ice.
I can put dry ice in my cooler, N requires a super heavy duty thermos and special handling.
I can hold (briefly) dry ice in my hand, if I drop/spill dry ice - no big deal, dust pan and broom.

Have fun

Dry ice or LN2 will both work in a cold trap for a rotary vane vacuum pump.

Check with your local supplier to see what size Dewars they can supply LN2 in. You want it as close as possible to your usage, as just sitting around it warms up and vents to atmosphere via the dewar PRV.

A cold trap has its own resistance to flow with attendant pressure losses, aside from the capital cost and cost to operate, so an alternative is picking up a new/used diaphragm or dry scroll vacuum pump that doesn't require a cold trap?

More money up front, but lower operating costs and higher performance without a fore trap.

I’ve thought of running a line through a freezer. Or maybe modding a small beer fridge with different refrigerant to get the temp down to -50. Anyone seen anything like that being used? Seems like such a waste. Once you have they system under vacuume there isn’t really any flow to cool if you have no leaks.

Fadedawg said:

Dry ice or LN2 will both work in a cold trap for a rotary vane vacuum pump.

Check with your local supplier to see what size Dewars they can supply LN2 in. You want it as close as possible to your usage, as just sitting around it warms up and vents to atmosphere via the dewar PRV.

A cold trap has its own resistance to flow with attendant pressure losses, aside from the capital cost and cost to operate, so an alternative is picking up a new/used diaphragm or dry scroll vacuum pump that doesn't require a cold trap?

More money up front, but lower operating costs and higher performance without a fore trap.

Click to expand...

I think I’m going to go with a diaphragm for now, I can definitely see saving all that money on coolant costs for condensing pretty fast