The Dwyer V4-2-U-AT is a Flotect vane operated flow switch with a brass switch body, a field-adjustable five-layer 316 SS universal vane and a SPDT (single pole, double throw) snap switch, rated to 1000 psig (69 bar) and supplied in a weatherproof, ATEX compliant, explosion-proof construction housing with a 1-1/2 in male NPT process connection and a 3/4 in female NPT conduit entry. A free-swinging vane attracts a magnet inside the solid metal switch body and trips the snap switch through a simple lever arm, so there are no bellows, springs or seals to fail. It monitors gases or liquids compatible with the wetted materials in pipe from 1-1/2 in to 8 in, and is usable in larger pipe sizes.
- Protecting pumps, motors and other equipment against low or no flow
- Controlling the sequential operation of pumps
- Automatically starting auxiliary pumps and engines
- Stopping liquid cooled engines, machines and processing when coolant flow is interrupted
- Shutting down a burner when air flow through a heating coil fails
- Controlling dampers according to flow
- Service with a brass wetted body, to a pressure limit of 1000 psig (69 bar)
- EU installations that require Directive 2014/34/EU (ATEX) compliant equipment for Zone 1 gas atmospheres
Magnetically actuated with no bellows, springs or seals to fail
A free-swinging vane attracts a magnet within the solid metal switch body and actuates the snap switch through a simple lever arm. There are no bellows, springs or seals to fail.
Field-adjustable universal vane
The five-layer 316 SS universal vane is configured in the field by removing vane layers as required for the pipe size, giving five vane combinations from 1-1/2 in through 8 in pipe and usable in larger sizes. See the actuation charts below.
Electrical assembly replaces without shutting the process down
The electrical assembly can be replaced without removing the unit from the installation, so the process does not have to be shut down.
Leak-proof body machined from bar stock
The brass switch body is machined from bar stock rather than cast, with a 316 SS vane block and a 430 SS magnet keeper.
ATEX compliant explosion-proof housing
Supplied as ATEX 2813 II 2 G Ex db IIB T6 Gb for Zone 1 gas atmospheres under EU-Type Certificate KEMA 03ATEX2383, with terminal block wiring inside the housing and a weatherproof enclosure designed to meet NEMA 4.
Installs with a thredolet, tee or flange
Mounts directly into the pipeline through a 1-1/2 in thredolet, a tee, a bushing or a flange, with a 1-1/2 in male NPT process connection. Rated to 1000 psig (69 bar).
| Service | Gases or liquids compatible with wetted materials. |
| Wetted Materials | Vane: 316 SS. Switch body: SAE 72 brass. Vane block: 316 SS. Magnet keeper: 430 SS. |
| Ambient Temperature Limit | -4 to 163 °F (-20 to 73 °C) |
| Process Temperature Limit | -4 to 163 °F (-20 to 73 °C) |
| Temperature Class | The temperature class is determined by the maximum ambient and or process temperature. Units are intended to be used in an ambient of -4 °F ≤ Tamb ≤ 163 °F. Units may be used in process temperatures up to 271 °F providing the enclosure and switch body temperature do not exceed 163 °F. The standard temperature class is T6, process temp ≤ 163 °F. |
| Pressure Limit | 1000 psig (69 bar) |
| Switch Type | SPDT snap switch. |
| Electrical Rating | ATEX models: 10 A @ 125/250 VAC (V~). |
| Electrical Connections | Terminal block. |
| Enclosure Rating | Weatherproof and explosion-proof. ATEX compliant construction: ATEX 2813 II 2 G Ex db IIB T6 Gb, -4 °F ≤ Tamb ≤ 163 °F, -4 °F ≤ process temp ≤ 163 °F. EU-Type Certificate No. KEMA 03ATEX2383. ATEX Standards: EN 60079-0:2012+A11:2013; EN 60079-1:2014. Designed to meet NEMA 4. |
| Process Connection | 1-1/2 in male NPT |
| Conduit Connection | 3/4 in female NPT |
| Vane | Five-layer 316 SS universal vane designed for 1-1/2 in to 8 in (usable in larger pipe sizes). |
| Set Point Adjustment | For universal vane: five vane combinations. |
| Mounting Orientation | Within 5° of vertical for proper operation. Units for horizontal installation (vertical pipe with up flow) available with the -V option. |
| Dimensions | 8 in [203.20 mm] overall length; 6-3/4 in [171.45 mm] housing to vane block; 3-11/32 in [84.93 mm] x 2-23/32 in [69.06 mm] housing; 1-5/8 in [41.28 mm] clearance required for cover removal. |
| Weight | 4 lb 8 oz (1.9 kg) |
Values shown in both charts are nominal. If normal flows exceed actuation rates by less than 10%, custom vanes are recommended. Figures are based on standard vertical installation in a 1-1/2 in thredolet in a horizontal run of pipe.
| Vane Layers Used | 1-1/2 in Pipe | 2 in Pipe | 3 in Pipe | 4 in Pipe | 6 in Pipe | 8 in Pipe | 10 in Pipe | 12 in Pipe | 14 in Pipe | 16 in Pipe | 18 in Pipe | 20 in Pipe |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 7-326.67-11.67 | 15-856.7-30 | 45-22167-83.3 | 95-40367-150 | 210-120800-450 | 375-1751417-667 | 600-3002267-1133 | 900-4503400-1700 | 1200-6004550-2267 | 1400-8005300-3033 | 2000-10007567-3783 | 2400-12009083-4550 |
| 1 and 2 | — | 7-426.7-15 | 23-1486.7-53.3 | 50-35190-132 | 130-90500-333 | 230-150867-567 | 450-2501700-950 | 650-3502467-1317 | 900-5003400-1900 | 1200-6504550-2467 | 1450-8005483-3033 | 1800-10006817-3783 |
| 1, 2, and 3 | — | — | 11-741.7-26.7 | 27-19102-71.7 | 80-60300-233 | 160-115600-433 | 300-1801133-683 | 450-2751700-1033 | 600-3502267-1317 | 750-4502750-2083 | 1000-6003783-2267 | 1200-7004550-2650 |
| 1, 2, 3, and 4 | — | — | — | 17-1265-45 | 60-45233-167 | 120-90450-333 | 230-150867-567 | 310-2001167-750 | 430-2801633-1067 | 550-3602083-1367 | 700-4502650-1700 | 850-5503217-2083 |
| 1, 2, 3, 4, and 5 | — | — | — | — | 40-30152-113 | 80-65300-250 | 135-100517-383 | 200-140750-533 | 290-2001100-750 | 360-2501367-950 | 460-3251733-1233 | 575-4002183-1517 |
Upper figure GPM, lower figure LPM. Each pair is the approximate actuation rate followed by the deactuation rate.
Actuation rates are based on cold water at a specific gravity of 1.0. For fluids of different specific gravity, actuation rates may be approximated by dividing the rate shown by the square root of the specific gravity.
| Vane Layers Used | 1-1/2 in Pipe | 2 in Pipe | 3 in Pipe | 4 in Pipe | 6 in Pipe | 8 in Pipe | 10 in Pipe | 12 in Pipe | 14 in Pipe | 16 in Pipe | 18 in Pipe | 20 in Pipe |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 32-1715-8 | 65-3230-20 | 210-105100-50 | 400-200190-90 | 950-475450-220 | 1550-850730-400 | 2400-13001100-600 | 3450-19001600-900 | 4700-26002200-1200 | 6400-35003000-1700 | 8000-44003800-2100 | 10000-55004700-2600 |
| 1 and 2 | — | 23-1310-6 | 120-7060-30 | 195-14090-70 | 550-375260-180 | 1100-700520-330 | 1850-1200870-570 | 2700-17501300-800 | 3400-22001600-1000 | 4800-31002300-1500 | 6000-39002800-1800 | 7400-48003500-2300 |
| 1, 2, and 3 | — | — | 60-4830-20 | 135-10060-50 | 375-265180-130 | 725-500340-240 | 1200-850570-400 | 1850-1300870-610 | 2600-18001200-800 | 3350-23501600-1100 | 4300-30002000-1400 | 5300-37002500-1700 |
| 1, 2, 3, and 4 | — | — | — | 65-5030-20 | 260-200120-90 | 500-400240-190 | 875-700410-330 | 1250-1000590-470 | 1900-1500900-710 | 2500-20001200-900 | 3100-25001500-1200 | 3900-31001800-1500 |
| 1, 2, 3, 4, and 5 | — | — | — | — | 130-10060-50 | 310-250150-120 | 650-525310-250 | 1000-800470-380 | 1600-1250760-590 | 2200-17501040-830 | 2800-22501300-1100 | 3550-28501700-1300 |
Upper figure SCFM, lower figure LPS. Each pair is the approximate actuation rate followed by the deactuation rate.
Actuation rates are based on air at standard conditions. For gases at other pressures, temperatures, or specific gravities, consult factory for equivalent flow approximations.
- Series V4 Datasheet (DS-V4 Rev. 4)
- Installation & Operating Instructions (Bulletin E-71 Rev. 10)
- Time Delay Relay Option Bulletin (E-71-TDR) – applies to -TRI / -TRD option units only
What pipe sizes does the V4-2-U-AT fit?
The five-layer 316 SS universal vane is designed for 1-1/2 in through 8 in pipe and is usable in larger pipe sizes; the actuation charts above run to 20 in. Remove only the vane layers that are too long for the pipe and leave the shorter layers in place to reinforce the vane, then resecure with the original 316 SS screws and lockwashers and lightly peen the screw ends so they cannot back out.
How is the V4-2-U-AT wired?
Terminal block connections inside the explosion-proof housing. The cable entry device shall be certified in type of explosion protection flameproof enclosure 'd', suitable for the conditions of use and correctly installed. Cable entry may exceed 158 °F (70 °C); conductors and cable gland rated 203 °F (95 °C) or higher shall be used. The switch is deactivated and the contacts are in their normal condition when there is no flow in the line, and the arrow on the side of the switch must point in the direction of flow.
What is the maximum pressure and temperature?
The brass body is rated to 1000 psig (69 bar). Ambient temperature limit is -4 to 163 °F (-20 to 73 °C) and the process temperature limit is -4 to 163 °F (-20 to 73 °C). Do not exceed the electrical, pressure or temperature ratings given on the product and in the instructions.
Is the V4-2-U-AT ATEX certified?
Yes. The -AT suffix is the ATEX compliant construction, marked ATEX 2813 II 2 G Ex db IIB T6 Gb for Zone 1, under EU-Type Certificate KEMA 03ATEX2383 to EN 60079-0:2012+A11:2013 and EN 60079-1:2014. IECEx certification is a separate construction and requires the -IEC suffix instead.
Can this model be ordered with two sets of contacts?
Not as supplied. The V4-2-U-AT carries the standard SPDT snap switch. A DPDT snap switch is a separate order code built with the -D suffix.
How should the V4-2-U-AT be mounted?
Within 5° of vertical for proper operation, normally in a 1-1/2 in thredolet welded into a horizontal run of pipe, with the body arrow pointing in the direction of flow. It can also be installed in a tee, a bushing or a flange. Units for horizontal installation in a vertical pipe with up flow are built with the -V option. Take extreme care when welding the fitting to the line so that it is plumb and level.
Specifications sourced from Dwyer datasheet DS-V4 Rev. 4 (8/25) and Bulletin E-71 Installation and Operating Instructions FR# 440629-00 Rev. 10 (8/21). Published 7 August 2026 by ZOT Supply.
1-Year Limited Warranty. ZOT Supply supplies the Dwyer Series V4 Flotect vane operated flow switch with a one-year limited warranty.
Per Dwyer Bulletin E-71: units in need of repair should be returned to the factory freight prepaid, and replacing the vane screws or lockwashers with substitute parts that may corrode and break will void the warranty. ZOT Supply is an authorized Dwyer distributor; contact us for return authorization before shipping any unit back.
- Product Type:
- Flow Switch
- Series:
- V4 Flotect
- Sensing Method:
- Vane Operated
- Media:
- Gases or Liquids
- Switch Type:
- SPDT
- Body Material:
- Brass
- Vane Type:
- Universal Multi-Layer
- Connection Type:
- NPT
- Connection Size:
- 1-1/2 in
- Pipe Size Range:
- 1-1/2 to 8 in
- Set Point Adjustment:
- Field Trimmable Vane
- Enclosure Rating:
- NEMA 4
- Hazardous Approval:
- ATEX Compliant
- Maximum Pressure:
- 1000 psi
- Max Process Temperature:
- 163°F
