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As a PTFE Ballvalve Seat and Valve Stem Sealing Gasket manufacturer, Gansu Juxiang Fluoroplastics Technology Co.,Ltd. molds and machines the sealing parts that sit inside ball valves: the seat ring, the stem sealing gasket and the support rings around them. Parts are produced from PTFE granular resin by molding, then finished to the seat pocket and stem geometry of the valve they will serve. We supply valve builders, valve repair workshops and process plants that need a seat with low friction, broad chemical resistance and stable seating force across thermal cycles.
Seats and stem gaskets are quoted as a matched pair against valve size, pressure class, medium and stem design, not as a single stock item. Molding, sintering and precision machining run across our Zhejiang and Gansu production bases in China, and custom parts are produced to drawings or samples.
Product Range and Where Each Part Fits
Ball valve sealing is a small family of parts with different wear paths. The seat carries the ball and controls leakage; the stem gasket seals the rotating shaft; support and thrust rings keep the seat from extruding under pressure. We produce them as one coordinated set so that interference and preload stay consistent after assembly.
- Seat rings — molded PTFE rings machined with a sealing face matched to the ball diameter and the DN of the valve.
- Stem sealing gaskets — flat, shouldered or convex rings that sit under the packing nut and seal the stem through quarter-turn operation.
- Thrust and anti-extrusion rings — back-up parts behind the seat where pressure class and temperature demand extra support.
- Related sealing parts — Modified PTFE Gasket for valve body joints, Filled PTFE Tube,Rod for machined seats, and PTFE Universal Seal where a valve uses a combined seat and stem seal.
Material Selection: Molded PTFE, Modified PTFE and Filled Grades
Seats are molded from PTFE granular resin, a route that gives a dense, low-porosity section and lets us hold the seat cross-section without machining away the skin. Molded PTFE brings the chemical resistance and temperature tolerance the valve needs; the values below are the property basis for the standard seat and stem gasket material.
| Property | Unit | Value |
|---|---|---|
| Apparent density | g/cm³ | 2.10–2.30 |
| Tensile strength (min) | MPa | 14.0 |
| Elongation at break (min) | % | 140 |
Where a valve runs at higher pressure, larger DN or a more aggressive thermal cycle, we move to modified PTFE or filled PTFE grades. Filled compounds raise compressive strength and reduce cold flow, which helps the seat hold its preload over time. The grade is chosen against the valve maker's pressure class and the process medium rather than applied by default.
Seat and Stem Gasket Dimensions
Seats and stem gaskets are molded close to size and then machined to the drawing. The nominal sizes below cover DN15 to DN150; intermediate sizes, larger valves and non-standard seat pockets are produced to the valve drawing or a supplied sample.
| Nominal DN (mm) | Seat OD (mm) | Seat ID (mm) | Seat height (mm) | Stem gasket OD (mm) | Stem gasket ID (mm) | Stem gasket height (mm) |
|---|---|---|---|---|---|---|
| 15 | 24 | 15 | 5 | 20 | 12 | 4 |
| 20 | 32 | 20 | 5 | 20 | 12 | 4 |
| 25 | 36 | 25 | 5.5 | 24 | 16 | 5 |
| 32 | 44 | 32 | 5.5 | 24 | 16 | 5 |
| 40 | 54 | 40 | 6 | 30 | 20 | 5 |
| 50 | 64 | 50 | 6.5 | 34 | 24 | 5 |
| 65 | 95 | 65 | 14 | 38 | 28 | 5 |
| 80 | 105 | 80 | 14 | 38 | 28 | 5 |
| 100 | 132 | 100 | 18 | 48 | 32 | 6 |
| 150 | 190 | 150 | 22 | 50 | 38 | 6 |
Values are nominal. Final seat height, face angle and stem gasket thickness are set from the valve drawing, because pocket depth and ball clearance determine how much preload the PTFE ring carries when the valve is assembled.
Application Fit: Media, Temperature and Cycle Duty
PTFE seats suit ball valves in chemical lines, water and wastewater, pharmaceutical process pipework, food-grade circuits and general industrial isolation service. The resin resists most acids, bases and solvents, and its low friction keeps operating torque down without external lubrication.
- Chemical and petrochemical lines — seats and stem gaskets for corrosive media where metal seating surfaces would corrode.
- Water and wastewater — larger DN seats for isolation valves on treatment and distribution lines.
- Pharmaceutical and food — smooth machined sealing faces that clean down and do not absorb process fluid.
- Thermal cycling — modified or filled grades where repeated heating and cooling would relax a virgin PTFE seat.
Temperature capability depends on valve design as much as on the resin. We confirm the seat grade against the continuous and peak temperatures stated in the enquiry, and against the line pressure at those temperatures.
Configuration and Machining Options
Each seat is configured to the valve rather than picked from a catalogue. The items below are agreed before machining and recorded on the drawing that goes to production.
- Seat cross-section — rectangular, chamfered or lipped, with the sealing face angle matched to the ball.
- Stem gasket profile — flat, shouldered or convex, with bore and outside diameter set by the stem and stuffing box.
- Tolerances — seat outside diameter, height, flatness and concentricity held to the valve maker's assembly clearance.
- Surface finish — sealing faces machined free of tool marks that would create a leak path.
- Marking and packaging — part number, DN, material grade and batch on the label, with seats packed to protect the sealing face in transit.
Quality Control, Documentation and Acceptance
Resin batches are checked before molding, and molding parameters are recorded for each production run. Finished seats and stem gaskets are inspected against the drawing for dimensions, flatness and surface condition, and the material is tested to the density, tensile strength and elongation values listed above.
Documentation follows the parts: material batch record, dimensional inspection report and handling guidance. Where a project calls for first-article inspection or a dimensional report against the valve maker's drawing, that is agreed at quotation stage and included in the delivery package.
Information We Use to Configure Your Solution
A quotation is only as good as the valve data behind it. These are the inputs we use to set the grade, dimensions and price of a seat and stem gasket set.
- Valve size (DN), pressure class and ball diameter.
- Seat pocket drawing or a sample seat, including pocket depth and face angle.
- Stem diameter, stuffing box dimensions and gasket profile.
- Medium, concentration and any suspended solids.
- Continuous and peak operating temperature, plus cycling frequency.
- Line pressure at temperature, and whether the valve sees vacuum.
- Annual quantity, batch size and spares requirement.
- Marking, packaging and documentation requirements.
Questions We Answer at Quotation Stage
What sizes of PTFE ball valve seats and stem gaskets do you produce?
Standard tooling covers DN15 to DN150, with seat outside diameters from 24 mm to 190 mm and stem gaskets from 20 mm to 50 mm outside diameter. Larger valves, intermediate sizes and seat pockets that differ from the nominal table are machined to the valve drawing or a supplied sample.
Are the seats molded or machined from PTFE sheet or rod?
Seats and stem gaskets are molded from PTFE granular resin and then machined to final size. Molding first gives a denser, more uniform section than machining from thick sheet, and it keeps the sealing face consistent from part to part.
Can you supply seats in filled or modified PTFE?
Yes. Filled PTFE and modified PTFE grades are available where a valve needs higher compressive strength, lower cold flow or better dimensional stability under thermal cycling. The grade is matched to the pressure class and medium rather than applied across an entire valve range.
What do you need to quote a ball valve seat and stem gasket set?
A drawing or sample of the seat and stem gasket, the valve DN and pressure class, the medium and operating temperature, and the quantity required. With those we confirm the PTFE grade, machining tolerances and documentation package, and return a quotation with the drawing for approval.
