What the tap holes do
Standard flanges have no provision for a pressure connection. An orifice flange adds two radial holes — one in each flange, on the same centreline, positioned per the chosen tapping standard — that connect to the transmitter's impulse lines. The flange set carries the plate, seals the joint and provides the pressure connection in one component.
Flange type
Orifice flanges are made in the same end-connection variants as standard process flanges. The end connection is chosen for the pipe schedule, service and how often the plate needs to come out for inspection.
| Type | Connection | When it's used |
|---|---|---|
| Weld neck | Butt-welded, tapered hub | Default for high pressure, high temperature or cyclic service — see our weld neck orifice flange page |
| Slip-on | Slipped over the pipe, fillet-welded | Lower-pressure lines where full weld-neck integrity isn't required |
| Socket weld | Pipe socketed in, fillet-welded | Smaller bore, higher-pressure lines where a butt weld isn't practical |
| Threaded | Screwed connection, no welding | Small bore, lower-pressure utility lines |
Jack screws
Some orifice flange sets add threaded jack-screw holes so the flanges can be pushed apart just far enough to free the plate, without fully removing the main bolting. Paired with a spectacle blind or paddle blind, this lets the line be isolated and the plate pulled for inspection without a full flange breakout. See our jack screw orifice flange page.
Dimensional standard
Flange dimensions, bolt circle and tap-hole size and location are governed by a dimensional standard — most commonly ASME B16.36 — separate from the standard that governs how the plate itself is sized (ISO 5167-2 or ASME MFC-3M). One is hardware, the other is the flow equation; a flange set that's dimensionally correct says nothing about whether the plate inside it is sized correctly, and vice versa.
Looking for a manufacturer to machine an orifice flange set to your process conditions and preferred standard? Send us your pipe size, class, fluid and flow range and we'll size and quote the set.