Vacuum Pump Questions

[position1]

Hi Everyone

I am doing my training and we have just been taught how to vac a system down.

But I have a few general questions about Vacuum pump use.

Is it bad (I am told it is) for my vacuum pump to suck no load (like open pipes).

When I first start to vac down the system (theres not much load on pump) a lot of oil mist comes from the exhaust of the vacuum pump. Is this normal ?

When I vac down a system, I connect the micron (mTorr) gauge between the service port (low side) and the blue manifold hose. But the gauge can be damaged by pressure and must be removed before charging the system ? When I disconnect the gauge a small amount of air is going to be drawn into the system, and again when I reconnect the blue manifold hose. Does this small amount of air matter ? Should I be connecting the Torr Gauge somewhere else to measure the vacuum so I don't have to disconnect before charging ? Should my hoses have better fittings, like some sort of low loss fitting ?

In training we are taught to vac down to below 500 microns (mTorr) for at least 15 minutes. This is easily achieved on the relatively small practice system and we were able to get down to below 50 in some cases. But we were told some compressor oils can boil at below 50 microns and we shouldn't go this low in practical situations. Is this correct ? What do people regularly vac down to and for how long ?

Thanks for your help.

Ben

[position1]

And I understand some people run the vacuum pump for long periods of time to pull down a large system or a contaminated system. Like running the pump for a few days isn't un-common.

Is this correct ? Is it bad to run my vacuum for long periods of time like this ?

[Peter_1]

[.... But we were told some compressor oils can boil at below 50 microns and we shouldn't go this low in practical situations. Is this correct

Just a quick reply to this one: the vacuum pumps we use never can boil the oil of the compressor.
Same like we can't brake the crankcase or break the sight glass by going to deep in vacuum level (heard all this rumors before)

[wandowski]

if i was you i would invest in a yellow jacket super evac manifold?!?!if you on ther website you can view the manifold,sits on top of your vacuum pump with 2 3/8 hoses coming off and can sit your torr/micron gauge on top,on a single split with the schrader cores removes in takes me around 30 mins to pull down and hold under 200 microns!good investment and then done need the gauges!or could just get a t piece and tap into you vacuum line and go that way!just get a 1/4 shut off valve and place in before you torr gauge and then save dissconnecting lines

[nike123]

http://www.refrigeration-engineer.co...7&postcount=16

http://www.refrigeration-engineer.co...3&postcount=28

http://www.refrigeration-engineer.co...80&postcount=9

[Peter_1]

The best place for the vac probe is as far as possible from the vacuumpump, so not on your pump nor on the LP service valve nor on the LP connection of the manifold.

[mbc]

You wrote : When I first start to vac down the system (theres not much load on pump)) this is not right when stating to vacuum system this time is your full load.
If you chose right oil for your vacuum pump do not worry about oil mist .
When you want to change your manifold hose to refrigerant bottle after you connect the hose lose hose from manifold side open a little gas ? lets air goes out then fix it and finally
Open the manifold vale very slowly . when your charging gas for first time to your system your system should be off until your pressure in both side ((system and bottle side ))is comes equal.
if you are working in large system during first charging it is better you charge from low and high side of your system (( suction and discharge )) your system should be off,
Do not charge liquid
As much as you can you should vacuum your system . it is true some people run vacuum for long time in large system But I found in small system it is more important than large system Because the condenser is small and small amount of air is very important

[position1]

Thank you all for your replies.

They have all been of great assistance.

The PDF about book " Vacuum for Service Engineers " link posted by nike was excellent.

I found the information about how the hose size affects vaccum pumps rather interesting.

Thanks again