A historical belt holder supports a running belt on freely turning rollers beside the machine pulley. It replaces a loose pulley, keeping the belt clear of the keyed pulley when the machine is disengaged.
Holder support and separate belt shifting
The holder frame shown here stays fixed. Its calculated roller load does not determine the force needed to move a belt onto or off the holder. A separate powered shifter would need its own travel, load and operating sequence.
For such a separate actuator application, use the linear actuator wiring diagram generator to plan electrical controls and compare force and stroke options in the FIRGELLI linear actuator range. The linear actuator replacement finder helps compare an existing actuator. Neither the holder calculator nor these product tools specify how to shift a running line-shaft belt.
Belt Holder Interactive Calculator
Explore belt speed, roller speed and ideal support loads in an illustrative three-roller holder. The holder is a fixed frame; it is not a spring-loaded belt tensioner.
Equation Used
- No slip or belt stretch; pulley contact diameters define belt speed.
- Equal tension in both spans at each holder roller; bearing losses neglected.
- The largest of the three roller loads is reported.
- Frame dimensions, parked machine pulley and shifting process are illustrative; no bearing rating or belt-life calculation.
Reference: Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement 1325, Wellington belt holder. The animation illustrates freely turning rollers in a fixed support frame.
The interactive diagram above shows the belt running on the holder rollers while the machine pulley is disengaged.
A place for the belt when the machine is disengaged
In the Wellington arrangement described by Hiscox, a fixed frame beside the machine pulley carries freely turning rollers. The belt is guided onto those rollers instead of a loose pulley. The holder supports the belt without driving the keyed machine pulley.
The animation shows a parked belt running from an upstream drive around three support rollers. A separate machine pulley sits behind the holder plane and remains clear of the belt. The frame stays fixed while its rollers turn. The three-roller layout illustrates the operating principle; its dimensions do not specify the Wellington product, and the shifting operation is not shown.
Historical use
Belt holders belonged to line-shaft machinery where the source could keep running while an individual machine was disengaged. The distinction is between a roller holder and a loose pulley: both provide a non-driving path for the belt, but their supporting construction differs.
Speed and roller reaction
Belt speed is v = πDN/60000 metres per second for drive contact diameter D in millimetres and speed N in rpm. With no slip, a roller of diameter d turns at ND/d rpm.
A roller that changes belt direction by β experiences the vector sum of the two adjacent span tensions. When both tensions equal T, the reaction magnitude is 2T sin(β/2). The calculator obtains β from the tangent belt geometry and reports the largest holder-roller reaction. This is not the belt’s tensile capacity or the bearing’s permissible load.
Worked speed example
A 160 mm upstream pulley at 200 rpm gives π × 160 × 200 / 60000 = 1.676 m/s. A 40 mm holder roller turns at 200 × 160 / 40 = 800 rpm. Doubling the entered span tension doubles the ideal roller reaction without changing either speed.
Roller diameter and support load
Small rollers turn faster for the same belt speed and bend the belt more tightly. Support force depends on both span tension and the direction change at the roller. The geometric model can show these relationships but does not establish acceptable belt construction, roller bearings or shifting conditions.
Belt-holder questions
Is this a spring tensioner?
No. The rollers turn freely in a fixed frame beside the machine pulley. They support the running belt while it is clear of that pulley.
Why is the machine pulley not moving?
The animation shows the belt parked clear of it. It is held stationary for clarity; a real disconnected machine may coast.
Why do small holder rollers rotate quickly?
The belt travels at the same speed over each contact. A smaller roller must make more revolutions to cover the same belt distance.
Original reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement 1325, printed page 324: the Wellington belt holder uses rollers in a fixed frame beside the pulley in place of a loose pulley.
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