Effect of belt driven pulley on motor

One of the possibilities is that, when the compressor starts to load-up, the torque required will be more than the three remaining belts can withstand, at which point they will begin to slip. The friction between slipping belts and the pulley wheels will generate heat, which could be enough to cook the belts and start to produce smoke or even a fire. At this point, shutting down the compressor is the only thing to do, apart from putting out the fire!

In the absence of a fire the motor will probably survive, and with slipping it won't be driven into full load and overload. The winding insulation issue is not relevant, unless it is damaged or destroyed by the fire from the slipping belts.

Some variable speed drives have a current limit set in them. Current is linearly related to torque so, if provided, setting the current limit to 3/4 of the full load value might succeed in preventing a fire at the expense of a drop in speed, and therefore performance of the compressor at times, which may or may not be acceptable to users downstream.

If the fourth belt is absent because of a temporary shortage of parts, then it may be possible to operate the compressor with only three for a short period by keeping the load on the compressor down, i.e. minimising the use of compressed air downstream. However, one cannot tolerate this situation for extended periods and fitting the correct fourth belt, thereby returning the machine to the original manufacturer's configuration, is highly recommended.

I take it that the pullies don't line up? I don't think it will affect it too much, maybe a bit more belt stretch, but if they are out of line, excessive belt wear and maybe bearing stress will occur! main thin is to get the pullies in line and straight with four belts!

I may be wrong but I don't see how it can possibly increase the load on the motor!

...the fewer the belts the less load on the motor...in the limit..no belts...no load!

The load on the belts will increase as the others have already said.

Four belts are used for better torque Transmission.If U use three it may still be sufficient but life of belts may be reduced in which case u may have to replace all 3 belts more frequently and saving by reducing one belt may be offset.Why do u want to reduce a belt?The other thing is belt pull on motor shaft may reduce and bearings may have a longer life.main factor is the capacity of 3 belts to transmit the torque.

the 4th belt allows the transmission of max torque to the compressor, so max pressure can be produced. the compressor running @ a reduced pressure, won't require the full load amps, or torque. If you try to extract the 100% power, from the motor w/only 75% of the power transmission [belts] capibility, slippage, smoke, failure, downtime & possibly fire.

the 4th belt allows the transmission of max torque to the compressor

Ha!... keep the 4th belt and remove the others!

Four belts are selected to reduce drive stiffness resulting from lower number of belts. You can drive power with one belt also but section of belt results in stiffned drive compared to more number of belts. Also as you increase number of belts, stiffness reduces and also belt section reduces. All section of belts have minimum pulley size. more the number of belts, smaller the belt section, smaller pulley diameter, lower tengentional speed of belt, lower belt wear.

Normally designer for compressor drive provides with factor of safety two due to flutuating load. If one belt is broken, this reduces to 1.33. So remaining three belts will wear faster.

There should not be any effect on motor or other electrical parameter like load current, winding insulaton etc.

By Nilesh D Mistry. email : nileshdmistry@yahoo.co.in

Dear RVB,

Number of grooves on the pulley are selected based on the power that it has to transmit. Grooves are also of different size and are designated as A, B, C or D and also FHP. So first check the belt to see its designation.

If you reduce number of belts, you would introduce improper transmission of power which will lead to slippage and may effect motor as well as compressor.

Capri, Crabtree and nesubra have said it all........no need for further answers......

... but that has yet to stop anyone in this forum!

For maximum usage, contact your belt manufacturer or supplier and insist on a matched set of belts. If you attempt to only replace one you will probably overtension the new belt while trying to match the tension to the other three. If you only adjust for the new belt the older ones will slip under load. Unless you order a matched set they may be off slightly and attempting to have even tension may be difficult. Temporarily running on three should cause no damage, but overtensioning to adjust for slippage may cause premature bearing failure.

As others have said, there will probably be no effect on the motor. In my experience you should replace all of the belts if one is defective, the others aren't far behind. Not to mention that multiple belts (that we use) are a matched set, designed and manufactured to specific specs. to ensure that each belt is doing it's equal share of the work.

Dear Friend,

In my opinion there will be no effect on motor or compressor side. The required power will be transmitted from motor to compressor in eitther way. The only thing that will suffer is the life of belts, will be shortened.

Due to possible belt slippage, the compressor may also run at lower RPM to achieve the desired/or rated efficiency.

4 belts are never loaded equally.

If 3 is doing the job -fine.

You can try with 2 at 2 adjacent grooves next to motor. If belts do not wear off rapidly ,2 will also be OK.

Stop there!

Nothing to harm motor.

Only belts' load carrying life!

there is a big chance that the belt would be overloaded and thus be damage...