FAQ: Mechanical Pumps - Types needed - new and used
Posted: Thu Oct 16, 2008 10:51 am
You need a vacuum pump! This is a must have item as it is called also a "fore-pump" in vacuum parlance.
A mechanical vacuum pump is needed and it must be a dual stage pump!
There are only two types normally used by amateurs and many professionals.
If you are serious about this effort, you must purchase a known good TC gauge, first!!!!
1. The direct drive pump
This pump uses a motor directly hooked via its shaft, inline with the pump, itself. These all have a carrying handle and all but the largest are portable type pumps, (actually, luggable). These pumps are typically rather noisy and rotate at high speed. Virtually all HVAC pumps are of this design type.
2. The belt drive pump
This is of a classical design type with a motor separated from the pump body, driven by a v-belt between pulley wheels on the motor and pump.
These pumps are never portable and are mounted on large steel base plates. This type pump usually runs much quieter than the direct drive and turn at a much lower speed. Generally they are two to three times the weight of a similar direct drive pump.
The Brand names that are best are Precision, Welch - Duo Seal, Edwards, Hyvac, Leybold, etc. These are Scientific pumps. Refrigeration pumps, as used in the HVAC business, are fine if they are two stage, as noted earlier, and are of sufficient pumping capacity. Robinaire and Yellow Jacket are typically good if two stage and not worn out or ruined, if purchased used.
The pumping capacity for any fusor mechanical pump needs to be at least 2 CFM for a demo fusor, but for real fusion in a really normal chamber of 6" or more, you will want something of at least 5 CFM Capacity.
New pumps cost between $300 - $2,000 of the type you need. Good rebuilt and warranted pumps in the 5CFM range can still cost $600 or more if purchased from a reliable seller of such pumps. Used, unknown condition pumps are all over the place from $25.00 to $300.00 in the size range above. Watch e-bay.
Buying a pump...........
Never buy a pump that is untested or un-gauged!! If you are buying locally, take your TC gauge with you. 1. Make sure the pump has oil in it. 2. Make sure it runs. 3. Put your gauge on it. 4. If it won't go to 100 microns rather quickly, you might pass it up or figure the oil is merely fouled. Tell the seller it must go below 50 microns. If still interested, offer half of what they are asking.
If buying off E-bay get a promise of money back if the pump will not go below 50 microns. Any back talk related to unable to test should send you packing. This is a clear sign the seller is a doltish idiot and just wants what he has, turned into money and to be done with you. Let some other poor slob who wants the seller's pump get flim-flammed.
Let us assume you now have a pump in hand...........
You bought it new? You bought it used?
What can you expect? How do you test it?
First, you should already own a good thermocouple gauge. Keep it simple and know that it is reliable and tolerably well calibrated. If you can't feel good about the gauge you will suffer mightily with false impressions about your new pump acquisition. Needless money and time will be spent if your gauge is off. New gauges are great and are money well spent as they can be assumed to be very close to accurate, as received.
If you have a new pump, you might be a bit more in luck, even with a questionable gauge. The assumption being that a new two stage pump will evacuate quickly to about 15 microns or less. If your used gauge says 200 microns and you have really tight connections to the gauge, you will know the gauge sensor is bad or grossly out of calibration.
Getting ready to test.......
The first order of business is to check the oil in the pump, new or old. make sure it is at the proper level.
If your pump is old and used make sure you can turn the shaft by hand. Hopefully, the pump is not seized. (You should have not purchased a seized pump in the first place!) If the oil level is low, do not top it off! Replace it! Drain the oil and put in clean oil or a flushing fluid oil.
If your pump is used, blank off the inlet and run the pump for about 2-4 hours. Dump the hot oil and if nasty or even clean-ish, put in new oil and now attach you gauge to the inlet.
If new, connect your gauge sensor to pump inlet with a very, very short piece of vacuum rated tubing. 2-3 inches is about right.
Testing the pump.........
Start the pump. you should hear a few minutes of the noisey lup-lup-lup pumping as the pressure drops. When the pressure bottoms, initially, the pump should get quiet. If it doesn't quiet down in a minute or so, then you have a leak in you head to gauge connections or an open gas ballast. Closing an open ballast will stop the noise and often let the pump dip another 5 microns or so.
After 4 minutes of pumping what is your pressure?
3-10 microns... Excellent! The pump must be brand new, a newly rebuilt one or you have just received a superb, well cared for, used pump.
10-15 microns... also great, but if a new pump you might check your gauge connections for a very minor leak. If a used pump, you still got a fantastic deal!! This is the range that most good pumps normally work at.
15-25 microns.... typical of a good, but well used pump. If used, take off the gauge and blank off the inlet (seal it off to vacuum tightness). NOTE: never let a running pump take in air from the outside world for any period of time, (Puts atmospheric water into the pump oil).
Let the blanked off pump run for 6 hours with the gas ballast open. Drain the formerly new oil or flushing fluid. Does it look nasty? Replace the oil and let the pump cool. Re-attach the gauge and close the ballast, then pump down and check the reading. If it is the same, your pump is just worn a bit and still serviceable for use with an added oil diffusion pump on the fusor. If the reading is lower, (Below the last reading by at least 5-10 microns), then you are getting the old pump back in shape...Good for you! You might blank off again and run the pump for 5 hours with the ballast open then refill one last time with fresh oil. YOU HAVE A GOOD PUMP. It was just filthy.
NOTE: Never run a pump for many minutes or hours with the gauge tube sensor close to the head!!! The oil vapors from hot oil might get inside the gauge tube and foul the thermocouple. A fouled gauge can be cleaned by dumping many loads of acetone or methyl-ethyl ketone into it, shaking it and dumping and then reloading, shaking and dumping, etc.
If you get 15-25 microns with a brand new pump, either you have a leak in your gauge line or the pump is not a very good scientific one.
25 - 50 microns.... A sad state of affairs. If used, your pump is either well worn or still filthy inside. Blank off as above and run for a few hours, dump the oil and put in fresh to try again. If the pressure is now lower, keep doing this until you can see no improvement. The point at which a pump is serviceable for fusor use with a diffusion pump added would be about 25 microns at the head, but you really want to see at least 20 microns or lower, if possible.
If your pump is new and you get 25-50 microns you might just have a bad pump or a very poor one. Note: Some new, cheaper, small refrigeration, direct drive pumps, (Chinese cheapo types), might only hit 25-50 microns right out of the box!
If you can't hit 50 microns and have a used pump, and have tried multiple oil changes and runs, then the pump is just worn out. Your options are, rebuild or start looking for a better pump.
Again, if you read 50 microns or higher, suspect the couplings to the gauge or the gauge itself. If the gauge is known to be perfect, then suspect the hookup line. If you are positive about the short line hookups, then you have a bad pump, for sure.
Finally, never hook a pump to your system without testing it first. In this manner, if you know your pump can hit 10 microns at the head, and when hooked to your fusor it will not pump the fusor to 100 microns, then you know you have a leak, either real or virtual somewhere in the plumbing.
Always test and adjudicate a pump at the head before use or hooking it into a fusor system.
Always know the state of your gauge. You can spend a lot of money and waste a lot of time rebuilding a perfectly functioning pump all because of a cruded up or defective $40.00 theromocouple gauge tube.
*****Important******
Finally!! you have your pump and it is tested. Now to hook it to your fusor, (demo), or your diff pump/turbo pump, (real fusor). The line or hose from you mechanical foreline pump must be kept short and fat!!! This cannot be over stressed. Ideally, you might not need over a 4 to 6 inch long hose, 1 inch in diameter. Position your chamber or secondary pump's outlet as close to you fore-line pump's inlet as possible within the mechanical structure of your finished vacuum system.
Richard Hull
A mechanical vacuum pump is needed and it must be a dual stage pump!
There are only two types normally used by amateurs and many professionals.
If you are serious about this effort, you must purchase a known good TC gauge, first!!!!
1. The direct drive pump
This pump uses a motor directly hooked via its shaft, inline with the pump, itself. These all have a carrying handle and all but the largest are portable type pumps, (actually, luggable). These pumps are typically rather noisy and rotate at high speed. Virtually all HVAC pumps are of this design type.
2. The belt drive pump
This is of a classical design type with a motor separated from the pump body, driven by a v-belt between pulley wheels on the motor and pump.
These pumps are never portable and are mounted on large steel base plates. This type pump usually runs much quieter than the direct drive and turn at a much lower speed. Generally they are two to three times the weight of a similar direct drive pump.
The Brand names that are best are Precision, Welch - Duo Seal, Edwards, Hyvac, Leybold, etc. These are Scientific pumps. Refrigeration pumps, as used in the HVAC business, are fine if they are two stage, as noted earlier, and are of sufficient pumping capacity. Robinaire and Yellow Jacket are typically good if two stage and not worn out or ruined, if purchased used.
The pumping capacity for any fusor mechanical pump needs to be at least 2 CFM for a demo fusor, but for real fusion in a really normal chamber of 6" or more, you will want something of at least 5 CFM Capacity.
New pumps cost between $300 - $2,000 of the type you need. Good rebuilt and warranted pumps in the 5CFM range can still cost $600 or more if purchased from a reliable seller of such pumps. Used, unknown condition pumps are all over the place from $25.00 to $300.00 in the size range above. Watch e-bay.
Buying a pump...........
Never buy a pump that is untested or un-gauged!! If you are buying locally, take your TC gauge with you. 1. Make sure the pump has oil in it. 2. Make sure it runs. 3. Put your gauge on it. 4. If it won't go to 100 microns rather quickly, you might pass it up or figure the oil is merely fouled. Tell the seller it must go below 50 microns. If still interested, offer half of what they are asking.
If buying off E-bay get a promise of money back if the pump will not go below 50 microns. Any back talk related to unable to test should send you packing. This is a clear sign the seller is a doltish idiot and just wants what he has, turned into money and to be done with you. Let some other poor slob who wants the seller's pump get flim-flammed.
Let us assume you now have a pump in hand...........
You bought it new? You bought it used?
What can you expect? How do you test it?
First, you should already own a good thermocouple gauge. Keep it simple and know that it is reliable and tolerably well calibrated. If you can't feel good about the gauge you will suffer mightily with false impressions about your new pump acquisition. Needless money and time will be spent if your gauge is off. New gauges are great and are money well spent as they can be assumed to be very close to accurate, as received.
If you have a new pump, you might be a bit more in luck, even with a questionable gauge. The assumption being that a new two stage pump will evacuate quickly to about 15 microns or less. If your used gauge says 200 microns and you have really tight connections to the gauge, you will know the gauge sensor is bad or grossly out of calibration.
Getting ready to test.......
The first order of business is to check the oil in the pump, new or old. make sure it is at the proper level.
If your pump is old and used make sure you can turn the shaft by hand. Hopefully, the pump is not seized. (You should have not purchased a seized pump in the first place!) If the oil level is low, do not top it off! Replace it! Drain the oil and put in clean oil or a flushing fluid oil.
If your pump is used, blank off the inlet and run the pump for about 2-4 hours. Dump the hot oil and if nasty or even clean-ish, put in new oil and now attach you gauge to the inlet.
If new, connect your gauge sensor to pump inlet with a very, very short piece of vacuum rated tubing. 2-3 inches is about right.
Testing the pump.........
Start the pump. you should hear a few minutes of the noisey lup-lup-lup pumping as the pressure drops. When the pressure bottoms, initially, the pump should get quiet. If it doesn't quiet down in a minute or so, then you have a leak in you head to gauge connections or an open gas ballast. Closing an open ballast will stop the noise and often let the pump dip another 5 microns or so.
After 4 minutes of pumping what is your pressure?
3-10 microns... Excellent! The pump must be brand new, a newly rebuilt one or you have just received a superb, well cared for, used pump.
10-15 microns... also great, but if a new pump you might check your gauge connections for a very minor leak. If a used pump, you still got a fantastic deal!! This is the range that most good pumps normally work at.
15-25 microns.... typical of a good, but well used pump. If used, take off the gauge and blank off the inlet (seal it off to vacuum tightness). NOTE: never let a running pump take in air from the outside world for any period of time, (Puts atmospheric water into the pump oil).
Let the blanked off pump run for 6 hours with the gas ballast open. Drain the formerly new oil or flushing fluid. Does it look nasty? Replace the oil and let the pump cool. Re-attach the gauge and close the ballast, then pump down and check the reading. If it is the same, your pump is just worn a bit and still serviceable for use with an added oil diffusion pump on the fusor. If the reading is lower, (Below the last reading by at least 5-10 microns), then you are getting the old pump back in shape...Good for you! You might blank off again and run the pump for 5 hours with the ballast open then refill one last time with fresh oil. YOU HAVE A GOOD PUMP. It was just filthy.
NOTE: Never run a pump for many minutes or hours with the gauge tube sensor close to the head!!! The oil vapors from hot oil might get inside the gauge tube and foul the thermocouple. A fouled gauge can be cleaned by dumping many loads of acetone or methyl-ethyl ketone into it, shaking it and dumping and then reloading, shaking and dumping, etc.
If you get 15-25 microns with a brand new pump, either you have a leak in your gauge line or the pump is not a very good scientific one.
25 - 50 microns.... A sad state of affairs. If used, your pump is either well worn or still filthy inside. Blank off as above and run for a few hours, dump the oil and put in fresh to try again. If the pressure is now lower, keep doing this until you can see no improvement. The point at which a pump is serviceable for fusor use with a diffusion pump added would be about 25 microns at the head, but you really want to see at least 20 microns or lower, if possible.
If your pump is new and you get 25-50 microns you might just have a bad pump or a very poor one. Note: Some new, cheaper, small refrigeration, direct drive pumps, (Chinese cheapo types), might only hit 25-50 microns right out of the box!
If you can't hit 50 microns and have a used pump, and have tried multiple oil changes and runs, then the pump is just worn out. Your options are, rebuild or start looking for a better pump.
Again, if you read 50 microns or higher, suspect the couplings to the gauge or the gauge itself. If the gauge is known to be perfect, then suspect the hookup line. If you are positive about the short line hookups, then you have a bad pump, for sure.
Finally, never hook a pump to your system without testing it first. In this manner, if you know your pump can hit 10 microns at the head, and when hooked to your fusor it will not pump the fusor to 100 microns, then you know you have a leak, either real or virtual somewhere in the plumbing.
Always test and adjudicate a pump at the head before use or hooking it into a fusor system.
Always know the state of your gauge. You can spend a lot of money and waste a lot of time rebuilding a perfectly functioning pump all because of a cruded up or defective $40.00 theromocouple gauge tube.
*****Important******
Finally!! you have your pump and it is tested. Now to hook it to your fusor, (demo), or your diff pump/turbo pump, (real fusor). The line or hose from you mechanical foreline pump must be kept short and fat!!! This cannot be over stressed. Ideally, you might not need over a 4 to 6 inch long hose, 1 inch in diameter. Position your chamber or secondary pump's outlet as close to you fore-line pump's inlet as possible within the mechanical structure of your finished vacuum system.
Richard Hull