1‑piece ball valve, SS316, 1/4" to 4"

A one‑piece low pressure ball valve has its body and end connections made from a single piece of material. That single detail drives everything else about it. Because there is no seam between two halves of the body, the solid cast body significantly decreases the risk of leakage — there is simply no body joint to weep from. It is the tightest of the three constructions.

The trade‑off is access. The valve trim and seals are inserted through one of the end connections during manufacture, and that is the only route in. It follows that the port size cannot equal the line size — so valves of this design do not have a port size equal to the line size and are always reduced bore. It also means the valve cannot be taken apart: when the seat eventually wears, you replace the valve rather than re‑seat it.

• Fewest leak paths of the three. One casting, so the only sealing points are the two threads you make up and the stem. That is the reason to specify it.
• ⚠ Reduced bore is not optional here. At 1/2" the bore is 9 mm against a 15 mm pipe — roughly 36% of the flow area. If that matters, you need the two‑piece. The numbers at every size.
• Not serviceable, by design. Specify it where nobody will ever open the valve. If seat replacement is foreseeable, the two‑piece; if it has to happen without stopping the line, the three‑piece.
• IMPA coded. 75 24 11 to 75 24 18 across 1/4" to 2" in BSPP, so it can be ordered against a marine code rather than a supplier part number.

Four angles on the same valve. All photographs of the stocked item, not renders.

The manufacturer’s sectional drawing. The callout numbers correspond to the part numbers in the table above.

• Read the drawing with the table. The section is the quickest way to see why the bore is reduced: the ball, seats and stem all had to pass in through one end connection, so the ball cannot be over‑sized.
• ⚠ The drawing carries 14 callouts; the parts list has 13. Items 1 to 13 match, but the drawing marks a 14th item on the handle that the published table does not name. We have not guessed at it — ask us and we will confirm with the factory before you order spares.
• ⚠ The drawing calls the handle span W; the size table calls it E. Same dimension, different letter — the manufacturer is not consistent between the drawing and the table. Use the E column in the size table for the figure, and check it against your swing clearance.
• Everything wetted is SS316 or PTFE. Body, cap, ball and stem in SS316; seat, seal gasket, stem seal and stem packing in PTFE. If you need to know what touches your fluid, that is the whole list.
• CF8M is the cast grade of 316, not a lesser material — it is the correct specification for a cast valve body and is chemically equivalent to wrought 316.
• The anti‑static device matters on hydrocarbons. A ball turning on PTFE seats is electrically isolated from the body; the SS304 anti‑static device (item 8) bonds the ball and stem back to the body so charge cannot build up. It is standard here, not an option.
• Handle in SS201, gland and nuts in SS304, spring washer in SS301. Lower grades than the body, on parts outside the pressure boundary — normal practice, and worth knowing if the valve lives somewhere salty.

This valve is used in service from −29 °C to 150 °C, and the environment temperature affects the working pressure across that range. The limit is set by the PTFE seat (item 3 on the parts list), not by the stainless body — SS316 is untroubled by 150 °C, but PTFE softens as it warms and the seat is the part holding the pressure.

Read off that curve and interpolated along its straight section. Treat these as approximate figures for selection and ask us to confirm any duty close to the limit.

• ⚠ A third of the rating is gone by 150 °C. 63 bar cold, 42 bar hot — 67%. If you sized on the catalogue figure and the line runs warm, the margin you thought you had is not there.
• Nothing is lost below about 20 °C. The curve is flat from −30 °C, so ambient and chilled service get the full rating. Derating only begins once the line is warm.
• ⚠ 150 °C is a wall, not a taper. The curve drops vertically to zero there. Do not design a small margin beyond it.
• Rated 1000 PSI, with the derating curve drawn to 63 bar. Both are the manufacturer’s figures, quoted as printed. For duty near the limit, give us the pressure and temperature together and we confirm against the specific part number.
• The same curve applies across the stainless range. It is the PTFE seat that governs, and the two‑piece and three‑piece use the same seat material. The range‑wide view.