V-Belt Installation & Tensioning

V-Belt Installation Check List 1) Disconnect and lock out power source. Observe all safety procedures. 2) Remove belt guard 3) Loosen motor mounts 4) Shorten center distance 5) Remove old belts 6) Inspect belt wear patterns for possible troubleshooting 7) Inspect and clean drive elements-bearings, shafts, etc. 8) Inspect sheave grooves for wear - replace if necessary 9) Preliminary sheave alignment 10) Identify proper replacement belts 11) Install new belts 12) Tension belts 13) Final sheave alignment 14) Replace guard 15) Start drive (look & listen) 16) Re-tension after 24 hours

Safety First Be sure to review and comply with all building and safety codes Disconnect and lockout the power supply

Inspect Drive Elements Inspect and replace faulty or damaged machine elements such as worn bearings or bent shafts

Relieve Belt Tension Loosen the drive take-up and move the sheaves closer together to facilitate the removal of the old belts and to insure installation of the new belts without damage

Inspect Drive Elements Sheaves should be cleaned of rust and foreign material

Inspect Sheaves Sheave condition and alignment are vital to V-Belt life & performance Never install new belts without a thorough inspection of the sheaves Look for worn groove sidewalls, shiny sheave groove bottom, wobbling sheaves and damaged sheaves

Select Replacement Belts Never mix new and used belts on a drive Never mix belts from more than one manufacturer Always replace with the right type of belt Always observe belt matching limits

Installing New Belts Place the new belts on the sheaves and be sure that the slack of each belt is on the same side Do not force the belts on the sheaves by using a pry bar or by rolling the sheaves

Check Sheave Alignment Sheave should be mounted as close to bearing as possible to reduce overhung load on bearing The straight-edge should make contact at two distinct points along the outside perimeter of both sheaves V-Belt sheave alignment should be within a tolerance of 1/16” per 12” of drive center distance

Sheave Alignment The straight-edge should make contact at four distinct points along the outside perimeter of both sheaves. 1 2 There should be no gaps between the sprocket and straightedge at 1-2-3-4 3 4 Proper Parallel Horizontal Vertical (Off-Set) Angular Angular (Pigeon-Toed)

V-Belt Tensioning Proper tensioning is the single most important factor necessary for long, satisfactory operation Too little tension will result in slippage, causing rapid belt and sheave wear and loss of productivity Too much tension can result in excessive stress on the belts, bearings and shafts

V-Belt Tensioning Tension-Finder A simple method to assure proper tensioning Easy and Accurate For use on individual belts or V-Bands Should not be used with aramid or glass cord belts

V-Belt Tensioning Using the Tension-Finder Step 1: Install belts loosely on the drive Step 2: Apply enough tension to take the slack out of the belts

V-Belt Tensioning Using the Tension-Finder Step 3: Scribe a line on the belt using the Tension-Finder as a square

V-Belt Tensioning Using the Tension-Finder Step 4: Place the Start Slot over the line

V-Belt Tensioning Using the Tension-Finder Step 5: With the line in the Start Slot, attach the spring to the belt For cog belts, the best place for the spring may be in the cog

V-Belt Tensioning Using the Tension-Finder Step 6: Scribe a line at the spring end of the Tension-Finder. Use this line as a reference point in case the spring slips off the belt

V-Belt Tensioning Using the Tension-Finder Step 7: Determine the required slot for your drive from the table. Then keeping the Tension-Finder snug against the clip, tighten the belt until the line has moved to the designated slot.

V-Belt Tensioning Using the Tension-Finder Step 8: Remove Tension-Finder hardware from the belt, tighten mounting bolts and replace belt guards. You’re ready to start the drive! Warning!! Remove all Tension-Finder hardware from the belt before starting the drive.

V-Belt Tensioning Special instructions for Cog Belts Place the spring in a cog groove

V-Belt Tensioning Special instructions for Cog Belts Put a dot in the start slot. Be careful not to catch the pen in the slot so you don’t pull the tip out of the pen.

V-Belt Tensioning Special instructions for Cog Belts Scribe a line through the dot. The line should extend across the width of the Tension-Finder.

V-Belt Tensioning Recommended tensioning slots for Tension-Finder The recommended slot numbers will provide an adequate level of belt tension on average drives. If more tension is required go to a higher slot number. For less tension go to a lower slot number.

V-Belt Tensioning Using the Spring Loaded Tensiometer 1. Measure the span length of the drive. Set the large “O” ring at 1/64” for each inch of belt span. For example, set the large “O” ring 1/4” for a span length of 16”, at 1/2” for a span length of 32”, at 1” for a span length of 64” etc.

V-Belt Tensioning Using the Spring Loaded Tensiometer 2. Set the small “O” ring at zero and press down the Tensiometer at the center of the belt span. A. On a single belt drive, depress the Tensiometer until the large “O” ring is even with the bottom of a straight edge placed on the outside rims of the two sheaves. B. On a multiple belt drive, depress the Tensiometer until the large “O” ring is even with the top of the next belt. Measure each belt in the drive. and take the average reading of all belt tensions.

V-Belt Tensioning Using the Spring Loaded Tensiometer 3. Remove the Tensiometer, and observe that the small “O” ring has moved from its original setting at zero to the number of pounds required to deflect the belt to the extent noted above. 4. Check this reading against the value of Pmin and Pmax calculated in Step 4 of the “Formula Method” or from the Table.

V-Belt Tensioning Strand Deflection - Formula Method This method is based on the fact that the force required to deflect a given span length by a given amount is related to the tension in the belt. Step 1. Measure span length (t) in inches as shown or calculate as follows: Where: t = span length, in inches C = center distance, in inches D = large sheave pitch diameter, in inches d = small sheave pitch diameter, in inches

V-Belt Tensioning Strand Deflection - Formula Method Step 2. Calculate the deflection distance by: t/64 = deflection. Note that the deflection distance is always 1/64” per inch of span length (for example, a 32” span length would require a deflection of 32/64 or 1/2 inch). Step 3. Calculate the static strand tension (Ts) per belt by the following formula: Design HP x K Ts = + Tc Q x S Where: K = value from the table depending on value of D - d C Q = number of belts/ribs on drive S = belt speed, feet per minute / 1000 Tc = add-on tension allowance for centrifugal force, from Table. Note: The value of Ts is for an individual V-belt.

V-Belt Tensioning Strand Deflection - Formula Method Step 4. Calculate the recommended minimum & maximum deflection forces (P), in pounds: Ts + Y (1.5 x Ts) + Y Pmin = Pmax = 16 16 Where: Ts = Static strand tension (from Step 3) Y = Constant from Table 30

V-Belt Tensioning Strand Deflection - Formula Method For drives using only one belt, and at least one shaft is free to turn, use the following for the deflection forces (P): Ts + tLr (1.5xTs) + tLY Pmin = Pmax = 16 16 Where: t = span length, inches (from step 1) L = belt pitch length, inches Y = constant from Table

V-Belt Tensioning STEP 5 Using a Tensiometer apply force to ONE belt of the drive, perpendicular to the span at its mid-point. Measure the deflecting force being applied when the belt has been deflected the distance calculated in Step 2 (use an adjacent belt as reference point; on single belt drives, use straight edge or taut string across sheaves). The measured force should be between the values of Pmin and Pmax calculated in Step 4. If the measured force is outside these values, adjust center distance to increase or reduce tension, and repeat above procedure. On multiple belt drives an average of readings on each belt is recommended.

V-Belt Tensioning STEP 6 NOTE: If new belts are being installed for the first time, it is permissible to tension as much as 1.33 x Pmax to allow for initial stretch and seating in the grooves. STEP 6 During the first 24 hours of operation, it is advisable to repeat the procedure in Step 5 at least once.

V-Belt Tensioning Operate the drive for a few minutes to seat the belts in the sheave grooves. Observe the operation of the drive under the highest load condition (usually starting). A slight bowing of the slack side of the drive indicates adequate tension. If the slack side remains taut during the peak load, the drive is too tight. Check the tension on a new drive several times during the first 24 hours of operation, by observing the slack side span.

V-Belt Tensioning Keep the drive free of foreign material which might cause slippage or damage to the belt and sheave surfaces. If a V-Belt slips, it is too loose. Increase the tension by increasing the center distance. Never apply belt dressing as this will damage the belt and cause early failure.

V-Belt Tensioning Excessive tension can be even more detrimental than too little tension not only on the belts but also the bearings and shafts. Indicators of excessive tensioning may be repeated belt breakage, excessive vibration, overheated bearings, whipping or bent shafts

V-Belt Tensioning Elongation Method Because belt elongation is related to the tension causing it, tape-measured lengths, both slack and tight, can be used to obtain proper Vee-Band tension. Note: The Tension-Finder is based on the elongation method.

V-Belt Tensioning Elongation Method STEP 1 Check sheaves to make sure they are properly aligned and that the grooves are not excessively worn (they should not be dished out more than 1/64”). STEP 2 Decrease the center distance until the Vee-Band(s) can be easily slipped into the sheave grooves. Forcing the belts on can damage the load-carrying cords and cause premature failure. STEP 3 With the Vee-Band(s) still on the drive at no tension, tape their outside circumference (slack O.C.).

V-Belt Tensioning Elongation Method NOTE: If you are tensioning a used belt, decrease the center distance until there is no tension on it; then tape the outside circumference.

V-Belt Tensioning Elongation Method STEP 4 Find the required static tension (Ts) per individual strand (rib) using the formula: Design HP x K Ts = + Tc Q x S Where: K = value from table depending on D-d C Q = number of belts S = belt speed, fpm/1000 Tc = add-on tension allowance for centrifugal force (See Table)

V-Belt Tensioning Elongation Method STEP 5 Find a range of recommended Static Strand Tensions: Lower value = Ts (from Step 4) Upper value = 1.5 x Ts STEP 6 Calculate minimum and maximum elongation band lengths for use in tensioning drive: a. From table, find length multipliers corresponding to the lower and upper values of Ts in Step 5. b. Multiply the slack O.C. found in Step 3 by the multipliers to find the minimum and maximum elongated band lengths.

V-Belt Tensioning Elongation Method STEP 7 Increase the drive center distance until a tape measurement of the bands O.C. is between the two values calculated for elongated band lengths in Step 6(b). STEP 8 Re-tension as required. A new Vee-Band may lose tension rapidly during the run-in period & will probably need re-tensioning. A Vee-Band that has been on a drive for some time may also require re-tensioning due to tension decay from normal use and wear.

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