Quick Guidelines for Determining Belt Tension on standard ...



Guidelines for Setting Proper Belt Tension on Standard V Belts

Belt tension is the single most important factor in ensuring long life of V belts, pulleys and supporting bearings. There are two general procedures for determining proper belt tension

- Deflecting the belt mid-span to pre-determined distance and confirming proper deflection force

or

- Measure the vibration frequency of the belt using the BTM-400PLUS

The purpose of these instructions is more specific to using the BTM-400PLUS belt tension meter.

This meter measures the vibration frequency of a V belt and, along with physical parameters of the belt, calculates the static strand tension per belt, Ts (lbf).

The mechanic then compares the measured value with the required value and adjusts the tension as necessary.

If the BTM-400PLUS belt tension meter is not available or if you wish to use the “deflecting the belt to pre-determined distance” procedure, you still need to calculate the value of Ts (lbf) by one of the methods below. Once that is determined, you then calculate the deflection force required by using reference material provided by the specific job.

STEP BY STEP INSTRUCTIONS FOR USING BTM-400PLUS

Step 1)

If not already done, set the Language (English), Measurement Units (lbf) and Engineering Units (U.S.) as shown on page 5 of the BTM-400PLUS manual

Step 2)

Go to the worksheet (page 5) and fill out all information shown. Pages 6, 7 and 8 of these procedures identify various types of belt designs and sizes. Use this information, if necessary to properly identify the belt

Step 3)

Determine the required value of the static strand tension per belt, Ts (lbf) by one of the three methods shown on pages 2, 3 or 4. If desired, an Excel spreadsheet has been created so that estimated values of belt tension can be obtained for the page 2 and 4 methods.

Step 4)

Measure the natural frequency of a belt strand using the Measuring Procedure of the BTM-400PLUS manual (page 7). This requires you to enter the belt weight per unit length and the free belt span, Lb obtained from the Worksheet. It is highly suggested to take several readings to get an average value. It is also recommended to take readings on more than one belt for pulleys with multiple drive belts. Refer to the troubleshooting notes on page 8 of the BTM-400PLUS manual.

Step 5)

Compare the measured value of the static belt strand with the required value and adjust the tension of the belts accordingly. See Note below

NOTE: The tension values calculated by these methods should be considered the MINIMUM values of belt tension. If installing new V belts, the mechanic should be aware that new belts will stretch over time. For that reason, most V belt manufacturers suggest tightening the belts to 1.3 times the required value of Ts

It is also recommended to run the new belts in for 12 hours and repeat the tensioning procedure again. It is not uncommon for MAXIMUM values to be 1.5 times the required value of Ts

Method 1 – Calculating Ts Using the Formula Method

-- Recommend Using the Attached Excel spreadsheet --

Ts = ((HP ∙ K) / (Q) (S/1000)) + Tc

Where

HP = Design horsepower of motor / driver from Worksheet

K = value from Table 29

Note that the K value depends on value of (D-d)/C calculated below

Q = number of belts on the drive

HP = ______________ hp

Calculate dimensionless number (D-d)/C = ________________

Values of D, d and C are from the worksheet. Use this number to determine K value below

K = _______________

Q = _______________

Calculate belt speed, S, feet per minute using the following formula and the values obtained from the Worksheet:

S = belt speed, ft/min = [(d) (RPM) (0.262)] = ___________________ ft/min

Divide belt speed by 1000 to get belt speed, ft/min/1000

S/1000 = _____________ ft/min/1000

Tc = Centrifugal tension add-on value from Table 31

Note that Tc depends on the value of S/1000 obtained above and the type/size of belt. Belt information is obtained from the part number designation on the belt or if necessary, use the information in the back of these instructions to determine the type/size of the belt that best describes the overall cross-section

Tc = _____________

Substitute the values into the equation to determine Ts

Ts = ((HP ∙ K) / (Q) (S/1000)) + Tc = _______________ lbf

Method 2 – Calculating Ts from Web Site Resource

Go to

The web site identified above will provide the static initial total tension, Tt (including other useful information) based on the HP, RPM, D, d, and C values obtained from the Worksheet.

The user should be aware that the calculations assume a standard type A 40˚ V belt is used. The calculated initial tension is also cumulative. That is, it is the tension force applied for all the belts. Therefore, in order to determine the required static strand tension per belt, Ts, it is necessary to divide the answer you get from the web site by number of belts, Q.

From web site, the total initial tension is Tt = _______________________ lbf

Divide this value by the number of belts to get the static strand tension per belt, Ts

Ts = Tt / Q = _________________ lbf

Method 3 – Calculating Ts Using the Alternate Formula Method

Ts = 16.5((2.5-N)/N) (HP/ (Q) (S/1000)) + (Cc + S2)/2

where

HP = Design horsepower of motor/driver from Worksheet

N = value from Table 29

Note that the N value depends on value of (D-d)/C calculated below

Cc = value from Table 30

Note that Cc depends on the type (cross-section) of belt. This information is obtained from the part number designation on the belt or if necessary, use the information in the back of these instructions to determine the type/size of the belt

Q = number of belts on the drive

HP = ______________ hp

Calculate dimensionless number (D-d)/C = ________________

Values of D, d and C are from the worksheet. Use this number to determine N value below

N = _______________ (From Table 29)

Cc = _______________ (From Table 30)

Q = _______________

Calculate belt speed, S, feet per minute using the following formula and the values obtained from the Worksheet:

S = belt speed, ft/min = [(d) (RPM) (0.262)] = ___________________ ft/min

Substitute the values into the equation to determine Ts

Ts = 16.5((2.5-N)/N) (HP/ (Q) (S/1000)) + (Cc + S2)/2 = _______________ lbf

WORKSHEET

From the motor nameplate or technical manual, obtain the following:

HP = Design horsepower = ______________

RPM of motor = ____________

Q = Number of belts = ____________

Referring to the figure below, measure C, d and D (L will be calculated):

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d = Diameter of the motor / driver pulley = _____________ in

(Note that the motor / driver pulley is usually the smaller pulley, but not necessarily)

D = Diameter of the driven pulley = _____________ in

C = Center distance between pulleys = ____________ in

Calculate the free belt span, Lb. As an alternative, you can just measure the free belt span, Lb

(For different size pulleys the free belt span, Lb will be slightly less than the center distance between pulleys, C).

Lb = Sqrt[C2 – [(D – d)/2]2] = ____________ in OR Lb (measured) = ______________ in

Measure the belt weight per unit length. This value will be inputted into the BTM-400PLUS

1) Record the belt length (in) = ________________ in

2) Divide by 12 to get length in ft, T = __________________ ft

3) Weigh the belt (single belt) to the nearest gram, Wgr = ____________________ grams

4) Convert to lbf by multiplying Wgr by 0.002204623, Wlbf = ____________________ lbf

5) Calculate belt weight (lbf) per unit length (ft) by dividing Wlbf by T, ft = ______________ lbf /ft

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(c) Banded V belt

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