The Dwyer V4-SS-2-D-U is a Flotect vane operated flow switch with a 316 stainless steel switch body, a field-adjustable five-layer 316 SS universal vane and a DPDT (double pole, double throw) snap switch, rated to 2000 psig (138 bar) and supplied in a weatherproof, UL and CSA listed, FM approved 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 316 stainless steel wetted body, to a pressure limit of 2000 psig (138 bar)
- Applications requiring DPDT switching
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 316 stainless steel switch body is machined from bar stock rather than cast, with a 316 SS vane block and a 430 SS magnet keeper.
Explosion-proof and weatherproof housing
Listed with UL and CSA for Class I, Groups C and D and Class II, Groups E, F and G, also FM approved, in an enclosure designed to meet NEMA 4. Wired with 16 AWG leads 6 in (152 mm) long.
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 2000 psig (138 bar).
| Service | Gases or liquids compatible with wetted materials. |
| Wetted Materials | Vane: 316 SS. Switch body: 316 SS (SAE 72 brass or 316 SS switch body per construction). Vane block: 316 SS. Magnet keeper: 430 SS. |
| Ambient Temperature Limit | -4 to 275 °F (-20 to 135 °C) |
| Process Temperature Limit | -4 to 163 °F (-20 to 73 °C) |
| Pressure Limit | 2000 psig (138 bar) |
| Switch Type | DPDT snap switch. |
| Electrical Rating | UL and FM models: 10 A @ 125/250 VAC (V~). CSA models: 5 A @ 125/250 VAC (V~); 5 A resistive, 3 A inductive @ 30 VDC. |
| Electrical Connections | 16 AWG leads, 6 in (152 mm) long. |
| Enclosure Rating | Weatherproof and explosion-proof. Listed with UL and CSA for Class I, Groups C and D; Class II, Groups E, F, and G. Also FM approved. 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-SS-2-D-U 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-SS-2-D-U wired?
Dual black, blue and red leads. Black is common, blue is normally open and red is normally closed; both poles are wired the same way. 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 316 stainless steel body is rated to 2000 psig (138 bar). Ambient temperature limit is -4 to 275 °F (-20 to 135 °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-SS-2-D-U ATEX or IECEx certified?
No. The V4-SS-2-D-U is the standard UL and CSA listed, FM approved explosion-proof construction. ATEX compliance requires the -AT option and IECEx certification requires the -IEC option. Units without the AT suffix are not Directive 2014/34/EU compliant and are not intended for use in potentially hazardous atmospheres in the EU.
What does the -D suffix mean on this model?
The -D suffix supplies a DPDT snap switch in place of the standard SPDT. It is wired with dual black, blue and red leads, connected in the same way as the single pole version.
How should the V4-SS-2-D-U 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:
- DPDT
- Body Material:
- 316 Stainless Steel
- 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:
- UL and CSA Listed
- Maximum Pressure:
- 2000 psi
- Max Process Temperature:
- 163°F
