Floating vs Trunnion Ball Valves: Selection Guide

The main difference is how the ball is supported and how pressure loads reach the seats. A floating ball can shift slightly toward the downstream seat under differential pressure. A trunnion-mounted ball is mechanically supported, while the seat arrangement supplies the movement and force needed for sealing. This affects seat loading and operating torque, but does not establish the valve's complete service limits.

For a procurement team, the useful question is which configuration meets the specified operating conditions, inspection requirements and maintenance plan. Start with service data and compare documented proposals. Neither the word floating nor the word trunnion is a substitute for a valve datasheet, an approved pressure-temperature rating or an agreed acceptance test.

A floating design is a useful candidate for compact isolation duties when the offered size, pressure, temperature and seat combination meet the project specification. Its construction can suit installations where a straightforward on-off valve is required. The downstream seat must handle the relevant pressure loading, so the manufacturer's allowable differential pressure and torque data matter.

Do not use an informal size or pressure cutoff to approve every floating valve. Compare the exact configuration, including bore, stem, seat support and sealing materials. A compact valve in a demanding service may require more detailed engineering than a larger valve in a mild service. Ask the supplier to identify any operating restrictions explicitly in the quotation.

Trunnion support carries the pressure load on the ball and can reduce the seat loading associated with an unsupported ball. This makes the arrangement worth comparing for larger bores and higher differential pressures. Seat geometry, springs and pressure action remain important: the actual sealing performance belongs to the complete design, not to the supports alone.

For pipeline or process isolation, ask for the proposed seat configuration, sealing direction and cavity-pressure management. Require a drawing or a clear technical description that matches the offered model. If a quotation lists optional features, distinguish what is included from what would require another design, additional testing or a change in price and delivery.

An RFQ should distinguish normal operating pressure from design pressure and from the pressure difference across the closed valve. These figures answer different questions. A procurement sheet containing only a nominal pressure class leaves the manufacturer without enough information to review the hardest opening or closing condition. Record the units and identify whether pressure values are gauge or absolute.

Temperature belongs beside every pressure requirement. ASME B16.34 covers matters including pressure-temperature ratings, materials, examination and testing, but the final valve also depends on its seals and construction. Request the rating basis for the offered configuration. Do not assume a class designation is a direct pressure value that remains unchanged at every operating temperature.

Describe the fluid composition, phase, solids content and credible changes during start-up or shutdown. A description such as gas or chemical is rarely enough. Give the supplier the project material class and relevant fluid data so the body, ball, stem, seats, packing and other wetted components can be reviewed together. Where the data is unknown, state that it remains an engineering hold point.

Compare soft-seated and metal-seated proposals against the required temperature range, leakage acceptance, wear exposure and operating cycle. Avoid treating a metal seat as automatically preferable, or a soft seat as suitable for every clean fluid. Record the proposed materials and the reason for any deviation from the project specification, then obtain the responsible engineer's approval.

Ask how the selected valve deals with pressure in the body cavity, which direction each seat seals and which conditions the supplier's test procedure covers. Do not infer an isolation function from the number of seats or from the presence of a drain connection. Terms used in a quotation should be tied to the project's specified standard, definitions and acceptance criteria.

If the process requires a particular block-and-bleed or double-isolation arrangement, include that requirement in the datasheet and request confirmation for the exact seat design. The operating procedure and pressure-relief arrangement also need project review. A generic product description cannot approve a valve for personnel isolation or establish a safe maintenance procedure.

Manual lever operation, a gearbox, a pneumatic actuator and an electric actuator create different installation and operating requirements. Request breakaway, running and closing torque for the proposed valve at the relevant differential pressure and temperature. Give the supplier the required operating time, available power or air supply, fail position and anticipated cycle frequency.

Review the valve and actuator as an assembly. The offer should identify the mounting interface, coupling, travel stops, accessories and any limits on the permitted stem torque. A statement that a trunnion valve has lower torque is insufficient for actuator selection. Require the sizing calculation and project-agreed margins, especially when starting after long idle periods or operating under unusual conditions.

Specify nominal size, required bore, end connection, flange facing or weld-end details and face-to-face dimensions. If the pipeline has pigging or other internal-clearance requirements, describe them rather than relying on the phrase full bore. Include the installation drawing when there are fixed pipe supports, limited lifting access or restrictions on actuator orientation.

A technically acceptable valve can still create an expensive site change if its envelope, weight or connection dimensions differ from the approved arrangement. Ask for a general arrangement drawing before final release. Confirm access to operating equipment, vents and drains, and identify any spares or removal clearances needed by the maintenance team.

State the applicable design and test standards with the editions required by the contract. API Specification 6D is relevant to valve procurement in its defined scope; additional project requirements must still be recorded. Fire testing, fugitive-emissions qualification, low-temperature testing and special material requirements should be requested separately when the project requires them, with evidence appropriate to the offered design.

Create a document index with the quotation. It may include approved drawings, material certificates, traceability records, inspection and test plans, pressure-test reports, coating records, actuator documents and installation instructions. Identify witness or hold points before manufacturing begins. An up-to-date management-system certificate does not replace product-specific records or prove that every optional requirement is included.

Send one consistent specification to each shortlisted supplier and ask for a clearly marked deviation list. Keep missing information visible so that quotations can distinguish confirmed requirements from assumptions. The following fields help the sales and engineering teams prepare proposals that can be compared on the same basis.

Place the technical offers side by side before comparing the bottom-line price. Check that size, class, materials, seats, actuation, standards and document scope match. Record exclusions, proposed alternatives and information still awaiting approval. A lower initial price may represent a different inspection scope or an omitted accessory rather than a comparable valve.

For example, if two suppliers quote the same line item but only one includes actuator sizing, witnessed testing and the requested material records, obtain a revised scope before making the commercial decision. Price and delivery should be confirmed against the final approved specification. Keep the approved deviation list with the purchase order so inspection and receiving teams can check the same requirements.

Is a trunnion ball valve always the better choice? No. Select the design that meets the actual duty and project requirements with an acceptable operating and maintenance arrangement. A more complex construction does not compensate for unsuitable materials, seats or missing test evidence.

Can a floating ball valve be used in a high-pressure application? Assess the manufacturer's validated range for the exact size, temperature, materials and seat design. There is no single class or size threshold that approves all floating valves or rules them out. Require the technical offer to demonstrate suitability.

Does an API 6D reference guarantee every requested test? No. Review the contract edition, applicable requirements, specified options and the supplier's inspection plan. A standard reference should be connected to the offered design and its records, rather than treated as a substitute for a complete purchase specification.

What should I send KEHUA for a selection review? Share the datasheet or the RFQ checklist above, including quantities and project requirements. KEHUA can review the relevant ball valve configuration and identify missing information before preparing a project-specific quotation.