Vacuum Pressure

The resultant vacuum pressure would likely be the same if you connected these in parallel. The draw-down time of the system might be cut in half, but the ending pressure would be the same. (Assuming the pumps are in fact the same.) If you are trying to improve on how quickly the system gets to a certain pressure, then a parallel installation would be preferred.

If you connected these in series, then you might reach a lower pressure, but probably not much better than you have already. Vacuum pumps tend to have some slip and get to a certain differential pressure before they cannot pump any more. Most can attain 28" Hg. 32" is vull vacuum, so you might get to 29" or 30", not that much of an improvement.

The third thing to consider is how much air leakage you have in the system. This may be the biggest driving force in what kind of pressures you can achieve. Air leaks into piping systems typically through flanges. If everything is tight, then little air leaks in, but if its an old piping system, then the vacuum leaks can be significant. Your pump can only move so much air, so it will draw down to a point where the air leaking in equals the capacity of the pump. Again, a parallel installation of the two pumps would be recommended here and you might in fact see a doubling of system performance. It all depends on how tight the system is.

I would check all the flanges in the system to make sure the bolts are tight and the gaskets are intact before going through the trouble of installing the pump. See what that gets you, then install the pump if you are still unhappy.

One thing to consider is: the Purpose of the lower vacuum level. If it is to achieve a higher FORCE on a surface, then sometimes it does hardly make a difference if your vacuum is eg 10^-4mbar or 10^-10mbar, beacuase it is the (force) difference between very little and very very little.

Rik.

If you are located at a high altitude the vacuum will be lower by a factor of the height. The answers given that there is a limit to vacuum are correct.

You can't really put them in series. The only time you will see two pumps in series is in a pump package where a roots blower is mounted on top of the mechanical pump. They are designed from the factory to work together...hence, the term "package". The blower increases pumping volume and therefore decreases pump down time, but the ultimate base pressure is determined by the mechanical pump. Generally, around 10 millitorr or so. Putting the pumps in parallel will only decrease your pump down time, but will not affect your ultimate base pressure. Unless you are evacuating a large vessel or chamber, you are wasting your time and money.

If you want to pump into the 10 X -4 Torr range or lower, you will have to add a high vacuum pump such as a cryo pump, turbo, or diffusion pump. Based on your question I kinda doubt you have the skill to do that so I would turn that over to a vacuum expert.

Not to put too fine a point on it, but once you you reach the base pressure of a good mechanical pump, you are no longer sucking anything. In fact, some would argue that you are never sucking anything. The pump is actually creating a pressure differential and the "sucking" is really the pressure attempting to equalize itself. Once you reach that crossover point in pressure, you are depending upon the random movement of gas molecules in the chamber to just "stumble" into the conduction path to the high vacuum pump.

'Nuff said.

And no offense to Del, but you will never remove all of the gas molecules from that jar unless you happen to be in outer space. Even then, its subject to debate. Space ain't empty.

i think you can introduce vacuum booster the way soap driers has to improve vacuum.

Depending on the purpose of the vacuum pumps in the system, you might be better looking at flow rates differential pressures, and system pressure losses.

The vacuum pump is a volume device trying to move X number of volume per minute across the pump. The flow rate is affeected by the differental pressure across the pump. The system pressure is affected by friction within the hoses and piping between the pump and the point of vacuum use. Leaks affect whether the volume is pulled at the point of use or from the interconnecting piping.

If two identical pumps are in parallel, the flow is increased, but the pressure differential across the pumps stays the same. Due to system effects, flow will not be doubled.

If two identical pumps are in series, the flow stays the same, but the presure differential is increased. Again due to system effects, tthe presssue will not be doubled (or in this case the vacuum)

can you please show the diagram of series connection and parellal connection of pump

I can't, I am not skilled at placing diagrams on this forum .

It would be similar to parallel and series resistors though.