compressor pump too big

[flip4eva83]

ok, so I had to order a new compressor. It got here today, upon initial inspection, this thing is HUGE. Much larger than what came off, too be expected, my original pump was 12.5cfm this one is a 17.5cfm. Now I wouldnt think too much about it and just put it on, BUUUT, the mounting wholes are about 3inches wider than the mounting wholes on the compressor. So here comes the questions (im sure some of you already know where Im going with this). Can I get a piece of 1/4 steel and create a larger mounting surface, bolting it between the pump and once its where it needs to be weld it permanently? Safe or spend the money to ship it back?

 

[stoveboltgunnut]

Before you go making a mount, do you have the motor to turn it?

 

[Packard V8]

I've put larger pumps on the same motor and used a smaller motor pulley to keep the same load. Larger pump can make same CFM at lower RPM.

jack vines

 

[flip4eva83]

yeah, it calls for a 5 hp motor and thats what I have.

 

[haveissues]

Check the rpm on the pump. The larger pumps run on much lower rpm as previously mentioned and you may have to change the pulleys. They are a lot quieter though.

 

[flip4eva83]

OK, glad I asked, because I have to buy a new motor pulley anyways. The motor says 3450rpm and the pump says 1650 rpm. The pump pulley is much larger than the stock one that came off.

 

[larry_g]

OK, glad I asked, because I have to buy a new motor pulley anyways. The motor says 3450rpm and the pump says 1650 rpm. The pump pulley is much larger than the stock one that came off.

Don't confuse motor and pump speed. If the new pump has a larger pulley you may already have the correct ratio. Look up or call the mfg and ask what the pump speed is supposed to be with a 5hp motor. Most mfgers have the same pump on different hp motors and just change the drive ratio to prevent the motor from exceeding its FLA rating. And what your doing its all about the amps.

lg
no neat sig line

 

[mayday0017]

Welcome to the forum, if you know the pump speed you want the pump to run at. Measure your pully on motor, measure the pully on pump, and write down RPM on motor. There are plenty of "calculators" online that will tell you what your final RPM will be with your current setup. From there you can adjust your pully sizes in the calculator until you get the final drive you are looking for.

Also it is worth me pointing out that your 5hp motor might not be 5hp... First if it's not 220v I believe it can't be 5hp so that is first check to see if it is. Second thing, look at the tag and see what the motor says the amps are, I believe they should be around 22 but I'm sure someone on here will correct me if I'm off on that part.

I just want to save you some hastle and make sure you have the correct equipment, as for making an "adapter" plate there is nothing wrong with doing this. Make sure your pully's line up and go with it. Also make sure of the stability of the compressor if it is vertical, they are already top heavy and people have been known to have them fall over. I would hate for you to put something offset and cause more stability issues and get someone hurt.

Hope this helps...

 

[flip4eva83]

Thanks for dropping in, I found an equation to figure out what pulley size I need. The motor is 208-230v and 15-16amps, says 5hp but as you pointed out, it may not be. Anyways, the equation is (motor rpm x motor pulley= pump rpm x pump pulley). I wanted the pump to run right around 1000 rpm so with my motor, my equation was 3450 x P = 1000 x 14.5 which gave me 4.2in motor pulley. I went with a 3.75in pulley which will put my pump rpm closer to 900 because max rpm is 1050 on the pump.

 

[truckdriver]

Thanks for dropping in, I found an equation to figure out what pulley size I need. The motor is 208-230v and 15-16amps, says 5hp but as you pointed out, it may not be. Anyways, the equation is (motor rpm x motor pulley= pump rpm x pump pulley). I wanted the pump to run right around 1000 rpm so with my motor, my equation was 3450 x P = 1000 x 14.5 which gave me 4.2in motor pulley. I went with a 3.75in pulley which will put my pump rpm closer to 900 because max rpm is 1050 on the pump.

15amps is not a true 5hp, but a 5spl. A true 5 will be about 23amps.

 

[GeneralDisorder]

Modifying the saddle to fit a larger pump is fine. Just make sure it is strong enough. I've seen a lot of cracked pump saddles.

You can't run that 5 HP pump at 900 rpm to a usable pressure on that 3 HP motor you have. You MUST take an amp reading to find the max pressure you can run. On a compressor the motor does not run at a constant load like most electric motor powered devices. The amps will increase as the pressure builds and you will most likely over-amp that motor before you hit 90 psi.

18 CFM is a nominal 5 HP pump. For most applications you can use the general rule of 4 CFM per HP so the most you can run that pump at with a 3 HP motor is an rpm equivalent to 12 CFM.

GD

 

[larry_g]

Modifying the saddle to fit a larger pump is fine. Just make sure it is strong enough. I've seen a lot of cracked pump saddles.

You can't run that 5 HP pump at 900 rpm to a usable pressure on that 3 HP motor you have. You MUST take an amp reading to find the max pressure you can run. On a compressor the motor does not run at a constant load like most electric motor powered devices. The amps will increase as the pressure builds and you will most likely over-amp that motor before you hit 90 psi.

18 CFM is a nominal 5 HP pump. For most applications you can use the general rule of 4 CFM per HP so the most you can run that pump at with a 3 HP motor is an rpm equivalent to 12 CFM.

GD

Very good advise from general disorder. You did not say what brand pump head you have but maybe you can interpolate some good data from the Quincy information here http://www.mesaequipment.com/Html/Products/Quincy/qr25_basic.html

Notice the different heads have a HP range they run at and also a speed range. The slower speed is for the min hp and the top speed is for the max hp. So if you fall in the mid range then you have to interpolate the HP/speed spec. As I said above you should be able to call the mfgr and get a speed spec for the HP motor you have.

lg
no neat sig line

 

[flip4eva83]

Ok so what it sounds like is the easiest route would be to get a pump that has the same specs as my original. I thought I could easily upgrade since I had to buy a pump anyways. This is what it is/used to be .http://www.homedepot.com/buy/maxair-60-galelectric-air-compressor-c4160v1-map.html#.UFvuso1lSZg. I would like to at least keep it the same if not upgrade its capabilities.

 

[larry_g]

Ok so what it sounds like is the easiest route would be to get a pump that has the same specs as my original. I thought I could easily upgrade since I had to buy a pump anyways. This is what it is/used to be .http://www.homedepot.com/buy/maxair-60-galelectric-air-compressor-c4160v1-map.html#.UFvuso1lSZg. I would like to at least keep it the same if not upgrade its capabilities.

Of course a direct replacement would be the easiest. However you can turn the compressor head you have a bit slower, it will last longer, be quieter, and still give you the same amount of air that the old pump did. You are limited by the motor HP right now and 3hp is a ~12 cfm compressor. But on the up side the motor on that thing is probably near end of life and when it goes then replace it with a true 5hp motor and speed the pump at at that time and your upgraded.

lg
no neat sig line

 

[flip4eva83]

OK, so with what I have do I have a usable rig?

 

[larry_g]

I would think so. Just monitor your current and adjust the drive pulley size if necessary.

lg
no neat sig line

 

[flip4eva83]

With what general disorder was saying, I wont get usable power at 900rpm, the max rpm on this pump is 1050. I have a 3.75 motor pulley

 

[larry_g]

What GD said was

You can't run that 5 HP pump at 900 rpm to a usable pressure on that 3 HP motor you have.

What he didn't say was that you CAN run that pump at ~600 rpm with a three hp motor and get good working pressure. You just cannot expect to get 17.5 cfm from it. By slowing it down you will get the 12cfm at pressure.

lg
no neat sig line

 

[GeneralDisorder]

You *can* run that pump on 3 HP.... but probably not with the motor you have unless you also re-sheave the pump to a still larger sheave. The fundamental problem here is that you bought a pump designed for a 5 HP, 1800 RPM motor. You have a 3 HP 3600 RPM motor and to get it slowed down enough to run on that small of a motor you will need a sheave on the motor side that's almost as small as the shaft diameter.... You will run into trouble getting the belt to not slip at startup and under load. It's not going to be fun making that combo work and frankly that home depot Chinese motor isnt worth the effort to use.

Basically you need to just do it right and get a 5HP 1800 RPM motor with 25 amps of capacity. I like a Baldor myself and they are readily availible for about $399. Get a proper sheave that's about half the diameter of the pump sheave to get it into the 900 rpm range.

GD

 

[sberry]

my original pump was 12.5cfm

This says it all.

 

[flip4eva83]

I know cheap isnt the route to go, but it would be cheaper for me to return the pump and go with something like this http://www.mastertoolrepair.com/1235-cfm-by-imc-p-1106.html?osCsid=g7iqock2ego5622purr7agl923. I just dont want to have more ******* in this then what I could go out and buy a new one.

 

[flip4eva83]

I know cheap isnt the route to go, but it would be cheapest for me to return the pump I have and get a smaller 12.5cfm. I just dont want to put more money into rebuilding this one then what I can go out and buy a new comparable unit for.

 

[PT Doc]

Of course a direct replacement would be the easiest. However you can turn the compressor head you have a bit slower, it will last longer, be quieter, and still give you the same amount of air that the old pump did. You are limited by the motor HP right now and 3hp is a ~12 cfm compressor. But on the up side the motor on that thing is probably near end of life and when it goes then replace it with a true 5hp motor and speed the pump at at that time and your upgraded.

lg
no neat sig line

That is a great idea. And when the motor farts out, get a 5hp off the bay and you'll be running more cfm and be quieter.