Selecting pipe diameter and vacuum pump 1

[Ivan Silva]

I have an application where I need to operate 112 suction cups and I need to know the suitable pipe diameter (All the suction cups are conect to a single main pipe, that’s the pipe I want to calculate) as well as the right size of the vaccum pump according to the time per cycle time I have. I have already tried to search for engineering manuals in the manufacturers but I couldn’t finding any numerical example only qualitatively aspect of the vacuum system design. My question do you guys know any source of information in order to guide me as how can I size the pipe and the vaccum pump?

 

[1503-44]

Use absolute pressures.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Ivan Silva]

That's not what I asked for.

 

[LittleInch]

So for me you first need to describe the operation.

So do all your 112 suction operate at the same time?

How do they work? attach all 112 and then pull the air out via a vacuum pump from the end of the big pipe? Or pull a vacuum in the big pipe and each of the suckers has its own solenoid ?

How fast do you need each to work?
What negative pressure do you need to get to?
What volume reduction occurs in the suckers?

Then you can start to work some of this out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Ivan Silva]

I know all that parameters are necessarily in order to size the pump what I asked for is some sort of source containing tables and formulas which would guide me towards the suitable vacuum pump. But since you bring all that questions here we go:

All the suction cups will operate at the same time.
All the suction cups are thread in vacuum chamber which is connected to main vaccum line. I can easily evaluate the volume of the vacuum chamber as well as the suction cup internal volume.
I need to create a -0,4 kPa vaccum pressure in 0,7 seconds

 

[3DDave]

https://www.leybold.com/en-us/knowl...s/vacuum-generation/how-to-choose-a-pump-size

 

[LittleInch]

What do you mean by -0.4 kPa?

Atmospheric pressure is approx 100 kPaa so do you mean 99.6 kPaa or 0.4 kPaa?

If the latter that looks unrealistic to me in that sort of time without connecting your system to a much larger vacuum vessel.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Ivan Silva]

Thank you, Dave! That will help me a lot.

Little, I mistyped it's -40 kPa

 

[LittleInch]

So 60 Kpaa?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Ivan Silva]

Yep

 

[LittleInch]

To do that in 0.7 seconds you probably need a big vacuum tank.

But vacuum suction is a well understood thing and lots of people make such systems. Have you asked them?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Ivan Silva]

I'm finishing the mechanical design which lay down on the project and I'll talk with vaccum system supliers but I would like to understand the physics behind this system.

 

[georgeverghese]

How much time do you have between getting the first batch of 112 cups down to 60kpa abs to the next batch of 112 cups ? That will set the capacity of the vac compressor to draw down the vac surge tank.
a) Vac tank is say at 20kpa abs, then some actuated valve opens to draw down first batch of 112cups to 60kpa abs in 0.7secs.
b) Pressure in the vac tank then rises from say 20kpa abs to say 40kpa abs.
c) Vac compressor draws down the surge tank from 40kpa abs back to 20kpa abs in xx secs. Vac Compressor draw down capacity will be highest at the start when tank pressure is 40kpa abs.
d) Surge tank then is ready for next batch of 112 cups

What is the time allocated xx? The longer xx is, the smaller the vac compressor design capacity will be.

So there are 2 lines to be sized also here (a) combined line from suction cups to tank (b) line from surge tank to vac compressor.

 

[Compositepro]

Suction cups are often equipped with ejector type vacuum pump located at the cup to avoid large diameter vacuum lines. These ejector pumps are powered by compressed air that can use small diameter tubing and create vacuum at the cup very quickly.

 

[Ivan Silva]

georgeverghese, thanks for your time to awnser my question! From the first batch to the next batch the process takes up to 8 secs but mostly of it the suction cups are been actuated, in fact only in the last 3,5 sec the suction cups are not been actuated. So in this case xx = 3.5 sec. Taking by your explanation, I think you are well understood in terms of vaccum systems, do you think this 3.5 sec are to short for the vaccum surge tank to "recharge"?

PS: I know this question is to vague since you don't how large needs to be this vaccum tank...

There is another problem, the product I need to manipulate (ladyfinger biscutit) is incredibly diffcult to handle since its surface is very irregular (it has a lot of rifts and suggar grains) and it is very porous.

If your curious in how the process works see this video because my applications is very similiar to it:

https://www.youtube.com/watch?v=znqSUwXYojY

 

[Ivan Silva]

Compositepro, Yep this ejector vaccum type are quite versitable but demains a lot from the pneumatic compressor especially when you have 112 vaccum pumps to suply. But the problem doesn't stops here the product has a lot of suggar grains and flour so the this ejector vaccum pumps would be clogged in short periods.

 

[3DDave]

A system like that won't use a vacuum pump but will instead use a blower fan to produce the pressure change. From your original number it's 0.06 psi. What they do in that example isn't to a pipe - it's to boxes with the large flex tubes coming into them and all the suction attachments directly attached to the boxes.

There should be a large valve inside to block the vacuum flow from the box with the tubes acting as reservoirs for low pressure.

Open the valves and air rushes into the hose and away from the ladyfinger biscuits. Close the vacuum valves and open vent valves and the biscuits get dropped.

 

[Ivan Silva]

Yep you are right 3DDave! My lack of knowledge in vaccum system made me make an mistake. Since the start of this discussion what I want was to size an blower fan not vaccum pump (I thougt it was the same thing) and yes this gantry works with a boxes (I call it vaccum box) in which suctions cups are attached to and this is what I'm using in my project. But even considering this misundestood my questions remains true. How can I size the blower fan, how large this flex tubes and vaccum box needs to be.