A small bypass cock can bridge a larger closed valve. This page follows the separate parallel-pipe arrangement illustrated by Hiscox in 1901. The calculator estimates the handle lever arm for an entered stem torque and perpendicular hand force; the animation shows the small bypass plug turning independently.
Bypass Cock Valve Interactive Calculator
Enter the required stem torque and available perpendicular hand pull to calculate a lever arm. Adjust the small bypass cock’s selected angle; the main valve is held closed. No flow split or pressure-relief performance is calculated.
Equation Used
- Hand force acts perpendicular to the lever; required breakaway torque is supplied by the user.
- The depicted small plug has a straight passage and turns from closed toward the selected angle. Internal proportions are illustrative.
- The main valve remains closed independently of bypass angle.
- No flow rate, pressure equalization time, leakage, valve capacity or pressure/temperature rating is calculated.
The historical bypass is a separate small valve around the main closure. The former three-way flow split has been removed; the handle lever calculation is retained and percentages now indicate travel only.
A separate bypass around the main valve
Hiscox’s Figure 1385 shows a small cock in a pipe that joins the line on either side of a larger valve. The small valve provides a separate passage when the large valve is closed. Its control is independent of the main valve.
The new drawing keeps that arrangement. The main body stays closed while an enlarged illustrative cutaway shows the small plug’s straight passage rotating. The handle turns with the plug. This is a functional historical illustration, not a dimensional drawing of the original component.
Understanding the parallel path
A bypass provides another connection between two points in a line. The capacity and intended use depend on the actual system; a small equalizing path is different from a full-capacity process bypass.
The picture demonstrates the connection only. It does not specify an operating sequence, safe isolation arrangement, relief device or a particular installation.
Handle length from torque and hand force
For force applied at right angles to the lever, torque equals force times lever arm. Convert the entered torque from ft·lb to N·m, divide by force in newtons, and convert the resulting metres to inches.
This calculation does not determine the required valve torque. It uses the value entered by the user. It also does not check stem strength, handle stiffness or available operating clearance.
The bypass travel result is 100 times selected angle divided by 90°. The main travel is fixed at zero in this demonstration. Neither output is a flow percentage; the former sine/cosine flow split was not supported by a valve or system model.
Example lever-arm calculation
At 50 ft·lb, the entered torque is 67.79 N·m. Dividing by a perpendicular hand force of 200 N gives a lever arm of 0.339 m, or 13.34 in.
Doubling available hand force halves the calculated lever arm. Changing plug angle changes selected bypass travel but does not change the entered breakaway torque or the lever calculation.
Bypass and diverter are different arrangements
This historical example has two separate valves and a small connecting pipe. A three-way diverter routes connections within a different valve arrangement. It should not be substituted into the illustration without changing the model and explaining the porting.
The present tool is useful for a simple torque-to-lever conversion and for visualizing a parallel path. Flow sizing requires actual valve data and system pressures.
Questions about the bypass model
Does opening the bypass close the main valve?
No. They are separate controls. The main valve is already held closed in this illustration.
Is bypass travel a flow percentage?
No. It is the selected angle as a fraction of a quarter-turn. Actual flow is not calculated.
Does the calculator predict breakaway torque?
No. It takes breakaway torque as an input and converts that to a lever arm for the entered perpendicular hand force.
Is this a pressure-relief-valve design?
No. It illustrates a manually operated historical bypass connection and does not model automatic relief, pressure limits or safe operating procedures.
Historical reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), printed page 335, Figure 1385: the separate small bypass pipe and cock bridging a larger valve. The internal plug cutaway and lever-force diagram here are explanatory additions.
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