A welded base pig signaler is an intrusive, bidirectional device welded to the pipe that confirms pig passage with a mechanical flag or an electrical switch. EMT’s SN2-TQZ needs no power for the flag version and works to 26 MPa.
Introduction
A welded base pig signaler is the cheapest reliable way to know a pig arrived. EMT fits the SN2-TQZ at launcher, receiver and key mid-line points, then lets the pig do the talking. When the tool passes, the trigger that reaches into the bore trips the indicator. The base is welded to the line, so there is no flange to match and no shut-down needed for the fitting itself.
Indicator Types
Three displays cover most needs. Type B is a flag that lifts from horizontal to vertical and resets by hand. And type C adds an SPDT switch that holds its state, useful for alarm or station logic. Type D is a digital clock that records the trigger time and stores it. Because the B flag has no wiring and no moving metal contact, it is treated as intrinsically safe in hazardous areas.
Pressure And Material
Working pressure runs 0 to 5 MPa, 0 to 16 MPa or 0 to 26 MPa, with custom designs on request. The base comes in ASTM A105N, A350 LF2 or 316L stainless. The plug and insert are built to the line so the wetted parts match the pipe. The trigger reaches the bore and its depth adjusts across 0 to plus or minus 10 mm to suit wall thickness.
Temperature And Rating
The unit works from minus 20 to 150 degrees C as a composite value, and EMT will confirm the figure for a specific medium. The electrical contact, where fitted, is rated 3A at 24V DC and the conduit thread is 1/2 NPT. The pipe opening for the base is at least 51 mm.
Installation And Care
Drill the hole to the model and wall thickness, set the trigger reach so the nose meets the bore, then weld the base. EMT supplies the steps and a dimension check so the trigger sits right. If the base shows a leak, the seal is gone and the unit returns for service; outer seals can be changed in the field.
Key Features
- Bidirectional trigger – Catches the pig in either flow direction.
- No power for flag – Type B has no wiring, so no spark risk.
- Welded to line – No flange to match, no shut-down to fit.
- Pressure to 26 MPa – Standard and custom pressure classes.
- Depth adjustable – Trigger reach 0 to +/-10 mm for wall thickness.
- Spare parts – Outer seals field-replaceable, kits available.
Specifications
| Attribute | Value |
| Model | SN2-TQZ (welded base) |
| Type | Intrusive, bidirectional trigger |
| Displays | B flag / C flag+SPDT / D digital clock |
| Working pressure | 0-5, 0-16, 0-26 MPa (custom on request) |
| Temperature | -20 to 150 deg C (composite) |
| Base material | A105N, A350 LF2, 316L (custom) |
| Trigger adjust | 0 to +/-10 mm |
| Contact rating | 3A / 24V DC, 1/2 NPT |
| Pipe opening | >= phi 51 mm |
FAQ
Does the flag version need power?
No. The Type B flag is a pure mechanical indicator with no electrical parts, which is why EMT classes it as intrinsically safe for hazardous areas.
What pressure can it take?
Standard builds cover 0 to 5, 0 to 16 and 0 to 26 MPa. EMT will design to a custom class if your line sits outside those ranges.
Can I add a switch after install?
The switch lives in the C or D display, chosen at order. If you later need an alarm, EMT supplies the matching display head for the same base.
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