Re: Pump Design
Dear kblack,
I understand that you want to create almost 100% vacuum. (tens of mbar inlet )
Have a look at the 2 links below.
http://eng-de.aerzen.com/content/view/full/174
http://www.gd-elmorietschle.com/
have a nice day
Teus ■
Teus
Thanks For The Quick Responce
I am not trying to create a vacuum , the inlet pressure is at 10mbar and I would like to boost this pressure to around 300mbar , I have looked at diphragm style pumps but wanted to see if lobe type pumps offered any advantages. Unfortunately I cannot find any information on how to calculate the operation. ■
Re: Pump Design
Dear kblack,
I understand.
You have an application with a required pressure ratio of 1.3/1.001 = 1.3.
This is a low pressure ratio, where a blower (lobe type pump) is a good choice over a compressor with internal compression.
A blower compresses isochoric (constant volume) and a diaphragm pump compresses between adiabatic and isothermal, which is an energetic advantage.
A blower is of a very simple construction with no reciprocating parts.
Also the application itself influences the choice s.a. the required amount of gas.
The following link does provide you the necessary information or otherwise contact a representative.
http://eng-de.aerzen.com/content/view/full/174
take care
Teus ■
Teus
Re: Pump Design
Hi there,
Do you have any flow range for the application and perhaps an idea if 300mBar is the design or the operating condition? That can all make a huge difference is choosing one technology over another. ■
Untitled
Dear Ralf / Teus
Sorry for the late responce.
I now have a little more information that might help.
The inlet pressure is at 10mbar and I would like to boost this pressure to around 300mbar , I have looked at diphragm style pumps but wanted to see if lobe type pumps offered any advantages.
The pump is required to deliver 5L / Min , at the moment I have calculated that my design would deliver more that this ( to overcome any slip ) and this is were I have a problem , I have a pump that is delivering x l/m into a pipe at a given speed.
If the slip area around the lobes is 15% of the outlet diameter do I design the pump to deliver 15% more to compensate for slip ? what happens if I slow the pump dowm at what point would the pump stop pumping , how can I calculate this.
Best Regards
kblack ■
Re: Pump Design
Dear kblack,
A volumetric rate of 5L/min is too small for a blower.
Volumetric efficiency will be an issue as you already noticed.
A peristaltic pump might be a good alternative for you.
Have a look at
http://en.wikipedia.org/wiki/Peristalticpump
for the working principle.
Success and take care
Teus ■
Teus
Untitled
Dear Teus
Can you give me more information on why this will not work for 5 l/m.
how can I calculate this.
I am looking at a minature application where the lobes rotate at relatively high speed to deliver the l/min required. I have scaled a pump down ( as I require a high quality / long life and the lobe concept seemed to fit the bill ).
From your answer I am unsure if I am incorrect in my assumptions.
Best Regards
kblack ■
Re: Pump Design
Dear kblack
The volumetric efficiency of a blower is represented by:
eta(vol) = 1 – leakage/displacement
eta(vol) = 1 – length * SQRT(pressure) /(length^3 * rpm)
or
eta(vol) = 1 – SQRT(pressure) /(length^2 * rpm)
The smaller the size, the lower the volumetric efficiency.
The higher the rpm, the higher the volumetric efficiency
To compensate a twice as small blower, the rpm has to be quadrupled.
Small blowers can be made, but the volumetric efficiency will be low.
If you have scaled down an existing blower, you also have to scale down the rotor gap and its effect on the rotor leakage.
The rotor leakage is not related to the outlet diameter at all.
A rotor gap slip area around the lobes of 15% of the outlet diameter (as you state) seems to me non-information, as we do not know the outlet diameter, which can actually be of any size.
For a calculation, see attachment
have a nice day
Teus
Attachments
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Teus
Re: Pump Design
There are practical limitations on scaling down a blower which you ought to be aware of. Five litres per minute against about 0.3 barg is so small that the fasteners maintaining the case seal will be bigger than a tiny rotor which can move fast enough to give the air displacment. In other words it'll look daft.
A Watson Bredel peristaltic pump might do your job but don't expect them to guarantee dry running hoses.
Is this really for a bulk handling application?
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Re: Pump Design
It is another variation of the simple gear pump. It is considered as a simple gear pump having only two or three teeth per rotor; otherwise, its operation or the explanation of the function of its parts is no different. Some designs of lobe pumps are fitted with replaceable gibs, that is, thin plates carried in grooves at the extremity of each lobe where they make contact with the casing. The gib promotes tightness and absorbs radial wear. ■
Re: Pump Design
Originally Posted by louispanjang
Seems unlikely 
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Pump Design
I am looking at positives and negatives of different pump designs, I would like to calculate the motor power required to drive lobe type pumps to see if there is any advantage over other pump designs. There seams to be lots of information regarding diphragm pumps with but does anybody know any useful links for lobe type pumps. I am considering low pressure gas tens of mbar inlet upto 0.3bar outlet ■