Four-part hygienic screw union in stainless steel: male part, liner, slotted round nut and gasket. Stocked in both the SMS and the DIN 11851 systems, which are not interchangeable.
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A hygienic union is a joint that can be broken by hand. It is made of four parts — a male threaded part, a liner, a slotted round nut driven with a C-spanner, and a gasket — and all four have to be ordered. It is specified where a line is stripped down for cleaning or where a valve, a pump or an instrument has to come out without cutting pipework.
The catalogue holds both systems, and they are two different joints. The SMS union, to SMS 1145 with its parts SMS 1146, 1147, 1148 and 1149, seals on a flat square-section gasket and sits on inch-labelled tube of 25.0, 38.0, 51.0, 63.5, 76.1 and 101.6 mm outside diameter. The DIN 11851 union seals on a D-ring gasket in a conical seat, uses a round thread to DIN 405-1 that can be run up by hand, and sits on EN 10357-A tube where DN25 is 29 mm outside diameter. Nothing crosses between them: not the tube, not the thread, not the gasket. The quickest way to tell them apart in the hand is the gasket — flat and square-section for SMS, a D-ring in a cone for DIN.
The two systems also carry different pressures. SMS 1145 is a nominal class 6 union. The DIN 11851 screw connection runs 40 bar from DN10 to DN40, 25 bar from DN65 to DN100 and 16 bar at DN125-DN150, usable to a maximum of 140 °C; published sources disagree at DN50, where the figure is given as either 25 or 40 bar depending on the maker, and that has not been resolved here.
State the system, the size — inch for SMS, DN for DIN — the end form (weld, or expanding for DIN), which of the four parts are required, the grade and the gasket material. For a 4 inch SMS union, state the thread size: two exist, 132 mm and 140 mm outside diameter, and they do not interchange, so a 4 inch SMS enquiry without the thread size cannot be quoted. Note also that DIN 11851 expanding parts are cut for the older DIN 11850 Reihe 1 tube, which differs from EN 10357-A below DN65.
| Union Make-Up | Four parts, all of which must be ordered: male threaded part, liner, slotted round nut and gasket. SMS: SMS 1146 male, SMS 1147 liner, SMS 1148 nut, SMS 1149 flat square-section gasket. DIN: Gewindestutzen, Kegelstutzen conical liner, Nutüberwurfmutter and D-ring gasket |
|---|---|
| Systems Stocked | SMS 1145 and DIN 11851. They are not interchangeable — tube outside diameter, thread form and sealing geometry all differ. The gasket is the quickest tell: flat square-section for SMS, a D-ring in a conical seat for DIN 11851 |
| Thread Form (DIN 11851) | Round thread to DIN 405-1, which is why a DIN 11851 nut can be run up by hand |
| Size Range (SMS) | SMS 1", 1½", 2", 2½", 3" and 4" on tube outside diameters of 25.0, 38.0, 51.0, 63.5, 76.1 and 101.6 mm. Two thread sizes exist in 4" SMS, 132 mm and 140 mm outside diameter, and they do not interchange |
| Size Range (DIN 11851) | DN10 to DN100 for expanding parts and DN10 to DN150 for welding parts, on tube to DIN 11850 / EN 10357-A |
| Pressure Rating (SMS 1145) | Nominal pressure class 6 bar at ambient temperature — the class of the union system, not a tested figure for a particular part |
| Pressure Rating (DIN 11851) | 40 bar for DN10-DN40, 25 bar for DN65-DN100 and 16 bar for DN125-DN150, usable to a maximum of 140 °C. The DN50 figure is manufacturer-dependent and is published as either 25 or 40 bar; this record does not choose between them |
| Material | Austenitic stainless steel; DIN 11851 parts are supplied in 1.4301 (304), 1.4307 (304L), 1.4404 (316L) or 1.4432 to EN 10088-3, and the nut is conventionally 1.4301 |
| Gasket | Natural or synthetic rubber, compatible with the product and the cleaning fluids and imparting no odour or taste. EPDM, NBR, VMQ, FKM or PTFE to be specified |
| Applicable Hygiene Standard | 3-A 63-04 Sanitary Fittings is the applicable class for this type of equipment. The goods are not asserted to carry the 3-A Symbol |
| Certification to Specify | EN 10204 3.1 inspection certificate for wetted stainless steel parts |
