How to decide the size of a receiver tank? 2

[miar1912]

I've encountered this issues last week and I'm not sure what the best way forward is. We are building materials manufacturing plant (have about 8 roll-formers right now). We don't have a proper air flow system and it was designed when we had about 4 machines, now we have about 8 machines and maybe 2-3 more to be added this year. The air compressor we use right now is a Campbell Hausfeld CE8001 and its motor had to replaced as it was heating up and started tripping the system. We were planning on adding a receiver tank(about 60 gal) at the other end of the production area and connect it back to the compressor to make a loop system but I'm not sure if its a good idea to invest in a receiver tank(maybe a larger capacity tank) or a new compressor.

I've done some reading around and now I have a whole bunch of questions. Some of the machines we received from other branches and they don't have any manuals so I've no idea how to go about calculating their cfm value. How do I calculate the cfm/scfm of a machine if I just have the psi values from the air regulators on the machines? We also have some packing tables and tools that need air supply, so those are to be taken into consideration; the compressor is rated at 36 scfm @ 90 psi, so what is the difference between scfm and cfm?; How to decide between a reciprocating or a screw compressor?

P.S. It's my first post over here and so I ended up posting it in the General Discussion. Sorry if this is confusing, I'll try to clear up any question if any. Any help is appreciated!

 

[hydtools]

You may find useful information here:

https://www.cagi.org/education/handbook.aspx

Ted

 

[dvd]

Attached is a straightforward treatment on receivers that I have saved in my files -

 

[miningman]

36 cfm is pretty small compared to the 600 cfm 125 HP units I am most familiar with. Im guessing you are dealing with only 10 or 12 HP. This is pretty low and does not imply major capital costs. IMO , a good sized receiver should be the first upgrade, and I would think a minimum of 120 gallons would be necessary. Make sure you allow for the regular draining of condensate, and depending on the distances you are moving air , a second receiver is often usefull. You might also investigate your line sizes, especially as the system demands are expanded..... install 2 inch lines to replace your 3/4 inch lines and youll be amazed at the improvements at the tools.

If you are running two or more compressors together , make sure you have check valves installed on all of them.

If you end up with two compressors make sure the unloading valves are set at different pressures, that way one unit will be adequate 85% of the time , with the second unit only kicking in when essential

 

[miar1912]

Thank you for the replies!!

@minigman

Yes, its only 10 HP and the tanks I'm looking at are not bank breaking. Yes, I'm mulling changing t larger sized pipe. Noted on the other points.

 

[LittleInch]

So your questions.

Some of the machines we received from other branches and they don't have any manuals so I've no idea how to go about calculating their cfm value. How do I calculate the cfm/scfm of a machine if I just have the psi values from the air regulators on the machines?

You can't unless you have some data from the regualtors. This is like saying "whats the power of the elctrical motor based on the voltage it I'm giving it?"

We also have some packing tables and tools that need air supply, so those are to be taken into consideration; the compressor is rated at 36 scfm @ 90 psi, so what is the difference between scfm and cfm?;

Scfm is cubic feet at "standard" conditions, usually something like 1.01 bar a and 15C. CFM is strictly just a volume per minute, but in air service is usually scfm, but with a small margin. It's pretty rare to find it is actually the cubic feet @ a certain pressure. 99% of the time CFM means CFM at "atmospheric" conditions.

How to decide between a reciprocating or a screw compressor?

Price? Oil content?

The ay you describe, the motor sounds like it was overloaded. Hence you need a bigger compressor.

There's no way we can see from here what your issue is, but miningman has some very good points, especially on size of tubing. The bigger the better and that essentially becomes a reciever all of its own.

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

 

[CWB1]

Draw a boundary diagram, this is a simple engineering problem. Receiver size is based on air demand (flow out) and compressor flow rate as a function of duty cycle (flow in). Too small of a receiver means your compressor cycles more frequently but for a shorter time, too large and it cycles less frequently but must run longer each time. Either extreme is capable of damaging the compressor, and obviously flow in should be greater than flow out to ensure a long compressor life. Given that your employer has purchased a compressor prepackaged with a receiver, unless you are having issues balancing the system then a second receiver likely isn't worth dinking with. Even if you are having balancing issues, in a small facility its likely worthwhile to simply upgrade the plumbing to allow greater flow. Given that you're burning up motors, before doing anything else I would check to ensure that you're not exceeding the existing compressor's nor its motor's duty cycle. I suspect you are, in which case a larger compressor would be the preferred upgrade and a larger receiver unlikely to fix the issue.

As to plant upgrades, if you have a machine's regulator pressure setting and pipe size you can either calculate or look-up flow on any number of standard charts available online from the various compressor manufacturers.

 

[keyepitts]

My vote would be to add another compressor along with larger delivery lines. If you've already had your existing compressor go down due to a burned up motor, you know what happens without any air for your production machines- people standing around and no product going out the door. A second compressor would add capacity and give some backup redundancy. Where I work we run two compressors with a lead-lag alternator that evens the wear on the compressors.

 

[miar1912]

@littleinch

Yeah that 1st question seems redundant with the kind of info I have and with the machines being older I was not able to get a proper value from the manufacturer. As for the 2nd question, I did some reading around and have the basic idea between scfm and cfm but the rating on the compressor is in scfm and I've got the ratings for the machines and tools that we use in cfm and so I was trying to put them convert them in the same thing so as to better quantify them. Lastly, I'd have see what kind of a second compressor we need as well as improving the overall piping of the system.

@cwb1

Yes, I'll try drawing the boundary diagram and check. As for exceeding the capacity of the compressor, the duty cycle is rated at 80% and I measured as to how much the compressor was running and its about 35-40% when we have most of the machines running so I'm assuming the compressor is still in a good shape it was some other issues in the electrical or something that messed up the motor (hopefully) and adding a secondary tank should solve the issue but I'm pressing for a second compressor as well.

@keyepitts

That is the exact issue i want to avoid so we don't have a situation where we just end up shutting down when the compressor shuts down. I'm looking at a second compressor with a similar lead-lag kind of arrangement.

Thanks for the suggestions everyone!