Too many grooves in my pulley?

[cokeguy]

Because of a belt slippage problem, I am thinking of ordering new 4-belt pulleys for one of my motor/pump combinations. Current configuration is a 2-belt (5VX type) 12 inch pulley for the 50 HP 1800 rpm motor, and a 18 inch pulley for the pump. During the last maintenance shutdown I simply changed belts and slippage was gone for the moment, but I fear that it could eventually return and cause problems again. Therefore, should I consider changing to 4-belt pulleys just to be on the safe side, or could the extra weight pose a problem for the motor? We are already close to the motor's amp limit.

According to my belt/pullet selction guide, 2 belts are enough, but I would like to be on the safe side without compromising motor performance.

Thanks for your comments...

 

[diskullman]

If you are going to order new pullies anyway, why not go to a positive drive, such as timing belt, HTD, or Gates Poly-chain.
Do you retension your belts after initial run-in?
Are your pulley grooves worn?
Have you tried a banded belt?
Why go from 2 grooves to 4? Why not 3 grooves?

Lots of possabilities.

Russell Giuliano

 

[tnkayaker]

Gates makes a belt that is "wrapped" with a cover that has a higher coeficient of friction. I'm sure Dayco or Goodyear have similar covers. I would use this type of belt when I designed mower decks. The cover is very good at handling shock loads.

Erik

 

[cokeguy]

Thanks for your comments, the rest of our pumps use standard 5VX belts and pulleys, they are slightly bigger pumps (from 75 to 150 HP) but they have at least 4 belts per pulley, and we never have belt slippage problems with them.

I while ago I came upon a certain motor manufacturer´s manual and it recommended 4 5VX belts for a 50 HP motor in general, that´s why I ordered the 4-belt pulleys, but then I came upon a more complete guide to belt and pulley sizing from TB Woods (Narrow Ultra-V Drives, section B1) and there it states that 2 belts per pulley (the original configuration) should be enough when all the variables come into play (pulley diameters, speed, etc..).

Therefore, I simply want to be aware of any ill-effects of using too many belts (in this case perhaps 2 extra belts) in my application or other typical applications. Thanks again.

 

[Tmoose]

Too many belts can make it easy to tension the bearings to death. I really like biggest allowable (for speed) diameter pulley/sheaves, and fewer belts. The notched v-belts work much better on smallish sheaves.

 

[ERT]

Two thoughts to add -

1. The motor pulley diameter must not be smaller than that recommended by the motor manufacturer, or else you risk overloading the motor bearings.

2. Belts for multiple V-belt drives must be installed as "matched sets", unless the belt manufacturer assures you that all their belts are length toleranced so that they are "matched". Some V-belt manufacturing techniques produce lengths that have relatively large variation and are post-production measured and graded into smaller tolerance bands. This is not a problem as long as sets are installed with the same length grade number.

Regards,

ERT

http://www.akeng.com

 

[Tmoose]

Note that accurate tensioning is at least as important than number and size of belts when it comes to power transmitted.
When establishing a test force and resulting deflection for accurate belt tensioning the power and belt span must be entered into the formula. Really Long belt spans don't look tight, even when tensioned to murderous levels.

 

[cokeguy]

According to our belt drive manual, and after performing and confirming all calculations with our specific configuration, it appears that two belts should suffice for up to a 60 HP load. Our pump motor is 50HP, so theoretically we are OK with just two belts. However, we plan to use 3 belts instead of two to have a margin for adjustment in case the slippage problem appears again during operation. In order to avoid overloading the bearings with too much tension, should we use a little less belt tension than the one recommended by the manufacturer? And how much less should we use? Or should we use the recommended tension? This is a pump that can´t be stopped easily because it affects the process too much, so we want to make sure we have the best possible setting at startup...

 

[diamondjim]

Can you also decrease the size of the pulleys
if you are insistant about using the extra
belt when you are already drawing the max
amperage from the motor?

 

[cokeguy]

Thanks diamondjim, maybe I didn´t understand your reply, but I can´t change the pulley ratio (pump and motor are on their design operating points), and installing larger pulleys with same pulley ratio is out of the question because of size restrictions.

 

[Tmoose]

I'd check with motor manufacturer about max radial load for excellent bearing life. Your belt driving motor probably should be using roller bearing at the drive end, not ball.
Installing the pulleys/sheaves with minimum overhang off the motor shaft (close to the motor housing) can significantly reduce bearing loading.

 

[pulleyguy81]

http://www.cdfracing.co.uk

can make any pulleys to spec -mainly deal with vee pulleys ,

james