Overview
The Dwyer FS-2-BSPT-2M is a Series FS-2 paddle (vane) flow switch with an SPDT snap switch rated 10 A resistive and 3 A inductive at 250 VAC. It has a 1" male BSPT process connection and a cable gland with 2 m attached wire leads, fits 1" through 8" pipe by trimming the field-adjustable vane layers, and is rated to 230°F (110°C) and 145 psig (10 bar) in a NEMA 4 (IP64) die-cast aluminum enclosure.
The Series FS-2 is an economical flow-proving switch for flow or no-flow duty in cold and hot water systems. Set point is tailored to the application in two ways: the vane is supplied as stacked layers that are trimmed to the correct blade length for the pipe size, and an adjustment screw shifts the trip point between the minimum and maximum flow settings published for that blade length. The aluminum weatherproof housing permits outdoor installation.
Specifications on this page are taken from the Dwyer Series FS-2 catalog page (Dwyer Instruments, LLC, rev. 11/2022) and the FS-2 Instruction Manual, Bulletin W-002 (FR# R5-443380-00 Rev. 1). Where the two differ the 2022 catalog page is used: it rates the enclosure NEMA 4 (IP64) where the 2014 manual lists IP64 only, and it adds the BSPT process connection and the optional conduit electrical connection. Verified August 2026.
The -BSPT-2M suffix combines the documented -BSPT process connection option from Dwyer catalog page 276 with a 2 m lead length that is not stated in either attached document; the lead length is taken from the Dwyer model descriptor for this part number.
Best For
- Boiler flow proving
- Hot water heaters
- Chillers
- Cooling lines
- Machinery
- Liquid transfer systems
Key Features
Field-Adjustable Paddle, 1" to 8" Pipe
The vane ships as stacked layers. Remove only the layers that are too long for the pipe, leaving the shorter layers in place to reinforce the vane, then resecure with the original screw and lockwasher and lightly peen the screw end so it cannot back out.
Field-Adjustable Set Point
An adjustment bolt sets the trip point. Fully tightened gives the minimum flow setting; fully loosened gives the maximum. Units ship fully tightened, in the minimum setting.
SPDT Snap Switch
The N.O. contact closes and the N.C. contact opens as flow rises to the actuation point, then returns to the normal condition as flow falls to the deactuation point. Rated 10 A resistive and 3 A inductive at 250 VAC.
NEMA 4 (IP64) Weatherproof Housing
Die-cast aluminum alloy enclosure rated NEMA 4 (IP64), suitable for outdoor installation.
Brass and Stainless Wetted Path
Forged brass body, tin-bronze bellow and stainless steel vane, rated to 230°F (110°C) and 145 psig (10 bar) on compatible liquids.
FS-2-BSPT-2M Configuration
This part number is supplied with a 1" male BSPT process connection and a cable gland with 2 m attached wire leads.
Technical Specifications
| Model | FS-2-BSPT-2M |
|---|---|
| Series | FS-2 |
| Service | Compatible liquids |
| Wetted Materials | Bellow: tin-bronze; Vane: stainless steel; Body: forged brass |
| Pipe Size Range | 1 to 8" (paddle field-adjustable) |
| Temperature Limit | 230°F (110°C) |
| Pressure Limit | 145 psig (10 bar) |
| Enclosure Rating | NEMA 4 (IP64) |
| Enclosure Material | Die-cast aluminum alloy |
| Switch Type | SPDT snap switch |
| Electrical Rating | 10 A resistive, 3 A inductive @ 250 VAC |
| Mounting Orientation | Vertical, on horizontal pipe runs |
| Set Point Adjustment | Four vane combinations plus an adjustment screw |
| Process Connection | 1" male BSPT |
| Electrical Connection | Cable gland with attached wire leads, 2 m lead length |
| Product Weight | 28.22 oz (0.8 kg) |
| Compliance | CE |
| Housing Width | 5-1/8" (130.2 mm) |
| Housing Depth | 2-13/32" (61.1 mm) |
| Housing Height | 3-1/32" (77 mm) |
| Mounting Face to Housing Top | 4-17/64" (108.3 mm) |
| Overall Height Above Vane | 5-49/64" (146.5 mm) |
Flow Rate Chart
| Pipe Size | Blade Vane Length in (mm) Dim. X | Minimum Setting GPM (LPM) | Maximum Setting GPM (LPM) | ||
|---|---|---|---|---|---|
| Actuate | Deactuate | Actuate | Deactuate | ||
| 1" | 1.34 (34) | 4.0 (15.0) | 1.8 (6.7) | 8.8 (33.3) | 6.6 (25.0) |
| 1-1/4" | 1.34 (34) | 5.3 (20.0) | 2.6 (10.0) | 11.4 (43.3) | 8.4 (31.7) |
| 1-1/2" | 2.24 (57) | 7.0 (26.7) | 4.0 (15.0) | 14.5 (55.0) | 11.4 (43.3) |
| 2" | 2.24 (57) | 14.1 (53.3) | 9.7 (36.7) | 31.3 (118.3) | 22.5 (85.0) |
| 2-1/2" | 3.46 (88) | 18.5 (70.0) | 15.4 (58.3) | 35.2 (133.3) | 30.8 (116.7) |
| 3" | 3.46 (88) | 27.7 (105.0) | 25.1 (95.0) | 52.8 (200.0) | 46.2 (175.0) |
| 4" | 3.46 (88) | 59.4 (225.0) | 52.8 (200.0) | 123.3 (466.7) | 114.5 (433.3) |
| 5" | 6.57 (167) | 52.8 (200.0) | 39.6 (150.0) | 132.1 (500.0) | 123.3 (466.7) |
| 6" | 6.57 (167) | 75.7 (286.7) | 52.8 (200.0) | 154.1 (583.3) | 140.9 (533.3) |
| 8" | 6.57 (167) | 184.9 (700.0) | 158.5 (600.0) | 396.3 (1500.0) | 374.2 (1416.7) |
Installation and Wiring
- Install with the housing arrow pointing in the direction of flow.
- Mount vertically on a horizontal pipe run; the switch will not work on vertical pipe.
- Keep at least 5 pipe diameters of straight run upstream and downstream, away from elbows, valves and pumps.
- Confirm the vane has full range of motion and does not contact the pipe wall, a bushing or a tee.
- Do not adjust the factory pre-set bolt; doing so can cause switch malfunction and may void the warranty.
| Brown | Common |
|---|---|
| Blue | Normally Open |
| Black | Normally Closed |
| Yellow/Green | Earth Ground |
Supplied with 2 m attached leads. Lead length is specific to this part number and is not stated in the Series FS-2 catalog page or instruction manual.
Documentation
Related Products
- Dwyer FS-21" male NPT process connection with cable gland and attached wire leads
- Dwyer FS-2-CND1" male NPT process connection with 1" NPT female conduit entry
- Dwyer FS-2-BSPT1" male BSPT process connection with cable gland and attached wire leads
- Dwyer FS-2-W81" male NPT process connection with cable gland and 8 ft attached wire leads
- Dwyer FS-2-VANEReplacement vane (paddle) assembly for the Dwyer Series FS-2 paddle flow switch
Frequently Asked Questions
What pipe sizes does the Dwyer FS-2-BSPT-2M fit?
1" through 8". The vane ships as stacked layers that are trimmed to the blade length listed for the pipe size: 1.34" (34 mm) for 1" and 1-1/4" pipe, 2.24" (57 mm) for 1-1/2" and 2", 3.46" (88 mm) for 2-1/2" through 4", and 6.57" (167 mm) for 5" through 8".
Can the FS-2-BSPT-2M be mounted on a vertical pipe?
No. Dwyer specifies that the switch must be installed vertically on horizontal pipe runs. Allow about 5 pipe diameters of straight run upstream and downstream of the switch.
What is the trip point and can it be changed?
The trip point depends on pipe size, blade length and the adjustment bolt. As an example, on 2" pipe with the 2.24" blade the switch actuates at 14.1 GPM (53.3 LPM) at the minimum setting and 31.3 GPM (118.3 LPM) at the maximum setting. Units ship with the bolt fully tightened, at the minimum setting. See the flow rate chart above for all pipe sizes.
What is the electrical rating and switch action?
SPDT snap switch rated 10 A resistive and 3 A inductive at 250 VAC. The N.O. contact closes and the N.C. contact opens when flow rises to the actuation point, and both return to the normal condition when flow falls to the deactuation point.
How does FS-2-BSPT-2M differ from the other Series FS-2 part numbers?
All Series FS-2 switches share the same body, vane and SPDT snap switch. The part numbers differ by process connection and electrical connection. This one is supplied with a 1" male BSPT process connection and a cable gland with 2 m attached wire leads.
Can the FS-2-BSPT-2M be repaired in the field?
No. Dwyer states the Series FS-2 is not field serviceable and should be returned if repair is needed; field repair may void the warranty. Contact customer service for a return goods authorization before shipping. The vane assembly itself is available as a service part, FS-2-VANE.
Dwyer Instruments (DwyerOmega) Limited Warranty
DwyerOmega warrants its products to be free from defects in material and workmanship under normal use for one year, or such other period as specified in a product-specific warranty supplied with the product. No product-specific warranty period is published for the Series FS-2, so the standard one-year term applies. Full terms, including claim procedure and exclusions, are published in DwyerOmega's Warranty policy.
Series FS-2 specific conditions. The Series FS-2 is not field serviceable and should be returned if repair is needed; field repair should not be attempted and may void the warranty. Contact customer service for a return goods authorization number before shipping, and include a brief description of the problem plus any relevant application notes.
Adjusting the factory pre-set bolt may lead to switch malfunction and possibly void the warranty. If the vane screw or lockwasher is lost, do not substitute other parts, which may corrode and break; doing so will void the warranty and might cause severe damage to equipment located downstream of the switch.
- Product Type:
- Flow Switch
- Series:
- FS-2
- Sensing Method:
- Vane Operated
- Media:
- Liquids
- Switch Type:
- SPDT
- Body Material:
- Brass
- Connection Type:
- BSPT
- Connection Size:
- 1 in
- Pipe Size Range:
- 1 to 8 in
- Set Point Adjustment:
- Field Adjustable
- Electrical Connection:
- Cable Gland with Wire Leads
- Lead Length:
- 2 m
- Enclosure Rating:
- NEMA 4
- Maximum Pressure:
- 145 psi
- Max Process Temperature:
- 230°F
