This page now separates the documented direct-acting regulator topology from valve selection and field advice. The connected cross-section shows a spring, diaphragm, stem, plug, seat and downstream sensing path; the calculator reports only declared pressure-times-area force values.
Declared Pressure-Area Force Ledger
Enter declared gauge pressure and two declared effective areas. The calculator reports P times the ordered areas and their midpoint; it does not solve spring equilibrium, plug travel, flow, set pressure or valve performance.
Equation Used
- P is declared uniform gauge pressure acting normally on an effective area.
- A and B are declared comparison areas; ordering them does not describe a moving diaphragm.
- The midpoint output is arithmetic only and is not an average over time or travel.
- Spring force, atmospheric reference, stem and seat forces, friction, preload and dynamic pressure are excluded.
- The connected animation is qualitative and does not map P×A to plug displacement.
- Flow, Cv, droop, hysteresis, cavitation, transients, materials, ratings, selection, installation, maintenance and safe operation are excluded.
Limits the calculator to an exact declared P×A force ledger and replaces mixed direct/pilot-operated performance and field advice with a source-grounded qualitative direct-acting topology.
Downstream pressure opposes an adjustment spring
Emerson and Spirax Sarco describe a direct-acting regulator in which downstream pressure acts on a diaphragm while a control spring supplies the opposing load. Diaphragm motion is transmitted through a stem to a restricting plug.
The animation shows that connected topology qualitatively. The numeric worksheet isolates only P times declared effective area; it does not claim an equilibrium position.
Use this page only for a pressure-area force identity
The worksheet compares force magnitudes for two declared effective areas at one declared pressure.
It cannot size, select, set, install, operate or troubleshoot a regulator or pump system.
Convert declared pressure and effective area to force
The unit identity is psi times square inches equals pounds-force. Actual equilibrium requires the opposing spring and other forces.
A transparent declared-force example
For P=100 psi, A=25 in2 and B=30 in2, the three declared force magnitudes are 2500.00 lbf, 3000.00 lbf and 2750.00 lbf at the midpoint area.
None is a valve rating or predicted stem force.
Pressure force alone cannot predict regulation
Real behavior depends on spring preload and rate, pressure references, plug and seat geometry, friction, flow, sensing arrangement and dynamics. Pilot-operated and direct-acting regulators also have different connected topologies.
The former municipal accuracy, Cv sizing, cavitation, product, installation, service-life, maintenance and troubleshooting claims are removed.
Pressure-area ledger questions
Is P times A the spring setting?
No; it is one declared force magnitude.
Does midpoint force describe diaphragm travel?
No.
Does the animation calculate plug opening?
No; its motion is qualitative.
Can this select a water regulator?
No.
Direct-acting regulator references
- Emerson, Principles of Direct-Operated Regulators: diaphragm force F_D=P2 A_D and equilibrium with opposing spring force.
- Spirax Sarco, SRV66 Installation and Maintenance Instructions: downstream pressure acts on a diaphragm against the control spring and closes the valve when it exceeds the set pressure.
- Emerson, DGX Series Direct-Operated Regulators Manual: sensing line, diaphragm, spring, stem and plug topology for a pressure-reducing regulator.
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