20 HP Magnetic Starters
Generic Magnetic Starters
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- Select the proper voltage and whether single phase or 3 phase.
- Also purchase the required heaters for your mag starter too.
Check valve problem
- If motor works fine and powers compressor pump until cut-out pressure, but when the compressor cuts back on and tries to recharge the tank, it is unable to start and stalls. (kicks the circuit breaker)
- Good indication that you have a defective check valve. Go to check valve test.
Capacitor Problem
- Remove capacitor covers. These are the “humps” on the back of the motor.
- Do they look overheated? Use a capacitor tester or if not available, test continuity across the leads of the capacitor.
Starter Switch Problem
- If your motor begins to start your compressor, but slows down, stalls and then kicks the circuit breaker, you could have bad starter points. Try the following:
- Remove the end of the motor that has the wires entering it. This should be held on with 4 long bolts and nuts that run the length of the motor. Use a screwdriver and small hammer to gently remove the end cover.
- 3. Under the cover, you will see a white plate that has the wire terminals. You should also see a round brown disc. Extending from the round disc you should see a long slender piece of copper or other material, the size of a wooden coffee stirring stick. At the end of this stick are electrical contact points. These points should be “closed”. Sometimes corrosion will build up on them. Take an emery file and file between the contact points to clean them. When the motor builds up speed, the small weights on the springs swing out and separate the points. This opens the circuit between the starter capacitor and the motor. One of the round hump capacitors helps to start the motor and when the motor reaches high enough speed the weights and springs open the points and the starter capacitor then stops sending a charge to the motor. At this point, the other capacitor, the run capacitor continues to keep the motor running. If there is corrosion on the points, the starter capacitor never kicks in and helps the motor to start.
Belts
- 90% of the time, low RPM is caused by OLD hard belts. Change the Belt(s). Tension should be about one half inch (1/2") deflection or give at a point halfway between pulleys when pressed with your thumb. Do not over tighten belt, it will break the crankshaft or burn up a bearing. Compressors do NOT squeal when the belts slip. It sounds like the motor is slowing down but what is really happening is the belt is slipping.
Motor HP
- Make sure you have the right motor pulling the Pump. If you have a 230 V motor converted to 120, you may have lost some pulling power. If it is the wrong motor not matching the correct motor pulley you may be overloading the motor. You may have an under-powered motor, or the motor is too small. Look at the amp rating on the motor plate and put an amp probe on the motor if and when it starts bogging down. The unit could be starved for power, have a weak ground, have low voltage, a poor connection or burnt contacts on starter or pressure switch etc…Amp probe will most likely show over-amping. You could also have under size wire from panel or too long of a run on wire itself from panel. If you don't have an amp probe it's recommended to take the motor in to a local repair shop or have an electrician come to your house for further diagnosis.
You're in the market for a new air compressor...what now? There are some things you'll need to know so you can find the air compressor that best fits your needs and your budget.
So, let's get started!
What brand of air compressor do you choose?
Is oil-free or oil-bath best?
Will I need a two-stage unit or is a single-stage unit sufficient?
How much CFM will I require?
How much PSI will I need?
If you're a contractor or use your air compressor in an industrial or commercial application, solid build quality, longevity and a reputable brand name should be key in your decision making process. Not to say this is unimportant for the homeowner or hobbyist, but there is a compressor for every demand and job out there; the more you know going into it, the easier it'll be when you're at the outlet about to make your purchase!
1) First, what is the application you'll be using your air compressor for?
If you're using the compressor to spray paint or sand blast, for instance, you'll probably want to get an oil-free unit, this way you won't have to worry about moisture getting into the line and mixing with your air. If you need high CFM (cubic feet per minute), then you can still go with an oil-bath compressor but you'll need to purchase it with a water trap and an oil/particulate filter to keep the compressed air nice and dry.
Oil-free units are great and very convenient as there is virtually no maintenance to worry about...there is no oil to change and you can operate the unit on an uneven surface, not something that an oil-bath unit can offer. Most oil-free units on the market, however, do not put out high CFM, generally 6 CFM or less. Also, these units are generally louder than oil-bath units, so if noise is a factor, go with either a “silent” oil-free compressor (the “JC10” Rolair unit or any of the California Air Tools units, for instance) or an oil-bath compressor. Oil-bath units are always recommended for longevity, and they simply put out a heck of a lot more CFM than any oil-free unit will be able to manage producing. Most contractors and all industrial applications and commercial garages demand a heavy-duty oil-bath air compressor as it will put out the CFM you need and will simply last a lot longer than any oil-free unit will. However, if you're a small contractor that has one or two workers, an oil-free unit may be sufficient. If you're simply using a trim gun to install trim in a kitchen, this doesn't demand high CFM so you can probably get away with using a smaller oil-free unit.
2) How much CFM is sufficient?
CFM (or Cubic Feet per Minute) is probably the most important specification you'll need to know when choosing an air compressor. Your application, whether it be a roofing nail gun, sand blaster or die grinder, will have a CFM requirement specification (you can find this in the manual for your tool). You need to choose an air compressor that at least meets that minimum CFM output. If an air compressor doesn't have the required CFM for your tool, it was run constantly and you risk burning the motor, pump or both, and your application will suffer for it as well. Be sure the air compressor puts out the required CFM (and ideally a couple more CFM) for your application! The CFM spec is related to duty cycle of a unit so we'll discuss that this term means now. Below is a very handy chart and info on what duty cycle means for an air compressor (and to give credit where credit is due, this very helpful information comes from VIAIR at https://www.viaircorp.com/tech):
Duty Cycle Reference Chart:
Duty cycle refers to the amount of time a compressor can be operated in a given time period at 100 PSI, and a standard ambient temperature of 72° F. It is commonly expressed in percentage format:
Compressor on time ÷ (on time + off time) = Duty Cycle %
Please Note: All compressors, regardless of rated duty cycle, require sufficient rest time in between cycles to allow for partial or complete heat dissipation. Heat dissipation rates may vary depending on ambient temperatures and operating conditions.
ONE HOUR DUTY CYCLE
| (100 PSI @ 72° F) | MINUTES ON/MINUTES OFF |
| 9% Duty Cycle | 5 Min. On / 55 Min. Off |
| 10% Duty Cycle | 6 Min. On / 54 Min. Off |
| 15% Duty Cycle | 9 Min. On / 51 Min. Off |
| 20% Duty Cycle | 12 Min. On / 48 Min. Off |
| 25% Duty Cycle | 15 Min. On / 45 Min. Off |
| 30% Duty Cycle | 18 Min. On / 42 Min. Off |
| 33% Duty Cycle | 20 Min. On / 40 Min. Off |
| 50% Duty Cycle | 30 Min. On / 30 Min. Off |
| 100% Duty Cycle | 1 Hour Run Time |
3) How much PSI do I need?
PSI (or Pounds per Square Inch) is how much pressure of air a compressor exhausts, whereas CFM tells you the volume of air produced. PSI isn't as important as CFM because most applications don't require high CFM. Any typical air compressor puts out at least 120 PSI, which is sufficient to run any nail gun, grinder or blow gun. There are some newer air compressors that put out high pressures of 225+ PSI, but these are purpose built for tools that take advantage of these higher pressures (and you only really see these in Japan and Europe for the time being). It's always a good idea to confirm, however, what the PSI requirement of your tool/application is prior, just as you would with the CFM rating.
4) Do I need a Single-Stage or a Two-Stage air compressor?
The different between single-stage units and two-stage units pretty simple. It doesn't have anything to do with the number of cylinders or heads the pump has. The main practical difference between the two is that a single-stage unit will [typically] operate at a lower PSI (max 155 PSI) whereas a two-stage unit will operate at 175 to 200 PSI). Also, a two-stage unit will recycle quicker (pump up quicker) and has a higher CFM rating than a single-stage unit. For applications/tools that require high CFM, such as a sandblaster or die grinder, it's probably best to go with a two-stage air compressor as it will recycle very quickly when called for more air, and will easily give you the volume of air you need to do the job efficiently. For most homeowners and hobbyists that are using small nail guns, blow guns or pumping up beach balls, a single-stage unit is definitely sufficient. Even most small contractors can get away with using single-stage units if they have a small crew.
5) Choose a reputable brand.
Look, I know that we live in an increasingly “throw-away” culture, where cheap Chinese air compressors are on the market, and even well-known brands are having components (if not whole units) built overseas with cheaper materials. And, sometimes buying cheap is worth it if you don't use the air compressor often, so what if the valves crack or piston ring(s) wear out? You can probably buy a replacement for the same amount as a repair would cost...I get it. However, it most cases it is certainly worth it to increase your budget and buy a unit manufactured by a reputable brand you trust; I'm thinking Campbell Hausfeld, Rolair, Jenny, Champion, Ingersol Rand and Coleman Powermate. Not only will these units typically be of a higher quality, but it's worth it just for the fact that most (but not all) units made by these manufacturers have replacement parts available, and offer great warranties. They also usually have a large network of authorized service centers available nationwide, so when you need to have the unit repaired, it's convenient to do so. It's the old adage, spend more now so you won't have to down the road.
I hope this beginner's guide to purchasing your first air compressor gave you some helpful advice and provided clear insight. The more you know going into the purchase the better, and knowing what you need will save you money now and later.
Thanks for reading!
Ever wonder how to calculate the CFM (Cubic Feet per Minute) output of your air compressor?
If you're not sure your old compressor is performing like it should or if you're just shopping for a new compressor, here's how so you can go in one step ahead!
Air compressors for residential and most commercial uses have notoriously inflated horsepower ratings. The specs and stickers on the unit are not always accurate, and add confusion instead of critical information to buying decisions.
The way to measure true power is to measure the time it takes to pump the reservoir tank of known volume from a known starting pressure to a known ending pressure. Then you can figure the true CFM from the difference in starting and final pressures, times the volume of the tank, divided by the time it took to pump up. You can also time the pump-up cycle from the cut-in to the cut-out pressure, since that's how one usually runs a compressor. These true performance measurements are impossible to fake.
- Determine the volume of your air compressor tank in gallons. This should be clearly marked on the tank itself by the manufacturer.
- Divide the tank volume by 7.48 (7.48 equals the number of gallons in one cubic foot.) The number that you get after the division is the tank volume expressed in cubic feet.
- Release the air from your compressor.
- Begin refilling the compressor with air. Record the amount of time that it takes to refill the tank while paying close attention to the compressor's tank gauge. You will need to record the psig (pounds per square inch) at two separate times in the refill process: once at the moment the compressor kicks in and once at the moment the compressor kicks out.
- Take the psig indicated on the compressor's tank gauge when the compressor kicked in and subtract it from the psig indicated when the compressor kicked out. For example, if the compressor kicks in at 75 psig and kicks out at 100 psig then the difference would be 25 psig.
- Divide the difference between the two recorded psigs by 14.7. The result will give you the amount of pressure added during the tank's filling cycle in terms of atm (atmospheric pressure).
- Take the volume of the tank expressed in cubic feet (calculated in Step 2) and multiply it by the amount of pressure added during the tanks filling cycle in terms of atmospheric pressure (calculated in Step 6). This is the number of cubic feet that your compressor pumps in the time it took for your tank to fill (recorded in Step 4).
- Convert this number to minutes. To do this, take the number of cubic feet found in Step 7 and divide it by the number of seconds it took to pump this amount. Multiply the result by 60 and you have the CFM of your air compressor.
Note: Any motorized device that takes power from a 120 VAC outlet, surely delivers less than about 2 HP, and likely far less. Why? Standard AC cords are limited to 15 amps of current, or about 1800 watts. At 746 watts/horsepower, and considering efficiency losses, 2 HP is all you can get, and even then the starting currents might be tripping circuit breakers.
Note: CFM ratings are meaningless without an associated delivery pressure. Thus, a compressor delivering 600 CFM is impressive, but if it uses a 1/3 HP motor then it only delivers 0.1 PSI.
This short video explains the basics on how to wire (or connect) a pressure switch to an electric air compressor.
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This short check valve video helps explain common symptoms of a bad check valve and how to test it.
This short video shows how to install or replace the valves on an EMGLO K pump.
This video gives an explanation of the advantages and features of a Dual Control Setup on a gas-powered compressor. Dual Control allows your compressor to operate in stop/start OR constant-run mode.
This video explains the basics of compressor maintenance. Follow these steps to keep your compressor running in tip-top shape!
Not sure if you need to replace your Safety Release Valve? Here's how to find out!
Click here to view technical document
Ever wonder how to calculate the CFM (Cubic Feet per Minute) output of your air compressor?
If you're not sure your old compressor is performing like it should or if you're just shopping for a new compressor, here's how so you can go in one step ahead!
Are your Rods frozen onto the pump Crankshaft but don't want to spend the money on a new pump? This instructional document will show you how to polish up the original Crankshaft when installing new Rods so you won't have to!
Click HERE for technical instructions
Just bought a new air compressor? Make sure you break it in to minimize damage to the pump and protect your investment!
This concise How-To doc gives pointers on breaking in your new air compressor or new pump.
Click HERE to view document
You bought an air compressor...now what?
This video gives you an explanation of each component on a few popular styles of air compressors and their functionality.
This is a comprehensive repair video that will show you how to install the Campbell Hausfeld WL211201SJ Valve Service Kit into an oil-free, direct-drive air compressor.
Which is really better? Does it really matter? We take both air compressors apart to show you what they are made of.
Is your old belt driven air compressor pump obsolete? We show you how to replace it with one that is similar in size.
Don't ruin your new piston ring and cylinder kit! There is a right way and a wrong way to install your new piston/cylinder kit for your oil free air compressor. We show you the correct way to install it.
Have you either had a compression fitting or needed to install one on a copper or aluminum pipe and didn't know how to measure it? It's easy. I explain how to figure the size you need in this tech video.
What's the deal with measuring pipe threads? Do you order the wrong size and wonder why? This very easy rule will save you headaches for the rest of your pipe measuring life. 3/4" NPT pipe refers to the nominal INSIDE diameter of the pipe, not the outside diameter.
This is a comprehensive repair video that will show you how to install the Campbell Hausfeld WL211201SJ Valve Service Kit into an oil-free, direct-drive air compressor.