The Dwyer DS-400-8-LV is a Series DS-400 In-Line Flow Sensor designed for installation in 8" pipe. The DS-400 is a heavy-duty averaging Pitot tube using 3/4 in diameter 304 stainless steel construction — built to resist the increased forces encountered at higher flow rates in larger pipe sizes (up to 24 in) where the standard DS-300 design would be insufficient. Multiple upstream and downstream sensing ports along the probe length provide effective averaged pressure readings, eliminating the need to traverse with a single-point velocity probe.
The DS-400-8-LV is inserted through a 3/4 in male NPT brass compression fitting (included) into a threaded branch connection (not included — typically a 3/4 in NPT female thred-o-let or saddle clamp welded to the host pipe). Insertion lengths up to 24 in are supported by the extra-strong 3/4 in stainless tube diameter. Pairs with any compatible Dwyer Magnehelic® or Capsuhelic® differential pressure gage, or any differential pressure transmitter with appropriate range. For 8" schedule 40 host pipe, the flow coefficient is K = 0.675; this is the -LV (less valves) variant — the same flow sensor without the integrated isolation valves and SAE 45 flared adapters, for installations where zeroing isolation isn't required or where external manifold valving is preferred.
Heavy-duty in-line flow measurement in larger 8" pipe applications — main process headers, utility distribution piping, large boiler feedwater and superheated steam lines, geothermal steam, cooling tower distribution, oil flow monitoring, and remediation applications. The 3/4 in stainless construction handles increased forces at higher flow rates that would exceed DS-300 limits.
Key Features
Multiple upstream and downstream sensing ports along the probe length — sized and positioned to provide effective accurate pressure averaging even at lower velocities. Eliminates the need to traverse the flowing stream with a single-point velocity probe, saving installation and commissioning time. Proven, reliable Pitot technology used in flow measurement for decades.
Flow coefficient K = 0.675 calibrated for use in 8-inch schedule 40 pipe — the constant used in the Dwyer flow equations to convert measured differential pressure (in inches W.C.) to flow rate (GPM for liquids, SCFM for gases, lb/Hr for steam). Refer to bulletin F-50 for the complete equation set.
3/4 in (19.05 mm) diameter 304 stainless steel sensor tube — constructed from extra-strong material to resist increased forces encountered at higher flow rates in larger pipes. Insertion lengths up to 24 in supported. Machined stainless head with brass packing gland compression fitting. Standard valves (when included) are brass with TFE seat and Buna-N O-ring, rated 200 psig at 200 deg F.
This -LV variant ships without integrated isolation valves at reduced cost. Appropriate for installations using external 3-valve manifolds for isolation and zeroing, or for applications where in-line valving isn't required. The 1/8 in female NPT pressure connections remain the same — valves can be field-added if needed.
Designed for compatible gases or liquids including water, steam (superheated, saturated, or geothermal), air (combustion, compressed, flue, stack, natural, flare), boiler feedwater, cooling water, and oils. Wetted materials: 304 SS sensor tube; brass compression fitting. Pressure limit 200 psig (13.78 bar) at 200 deg F (93.3 deg C).
Mounting orientation matters: for air or gas flow, install the sensor in the upper quadrant of the pipe (so condensate drains back to the pipe). For liquid or steam flow, install in the lower quadrant (so air bleeds back to the pipe). The side connection is high pressure (HP) and should be pointed upstream; the top connection is low pressure (LP).
Technical Specifications
| Specification | Value |
|---|---|
| SKU | DS-400-8-LV |
| Series | DS-400 |
| Product Class | Averaging Pitot In-Line Flow Sensor |
| For Host Pipe Size | 8" |
| Host Pipe Schedule (K Factor Calibration) | Schedule 40 up to 20 in; Std wt for 24 in |
| Flow Coefficient (K) | 0.675 |
| Service | Compatible gases or liquids |
| Sensor Tube Material | 304 Stainless Steel |
| Compression Fitting Material | Brass |
| Process Connection | 3/4 in male NPT compression fitting (brass packing gland, included) |
| Instrument (Piping) Connections | 1/8 in female NPT |
| Valve Configuration | No integrated valves (-LV configuration) |
| Valve Rating | N/A (no valves) |
| Adapters Included | None |
| Pressure Limit | 200 psig (13.78 bar) at 200 deg F (93.3 deg C) |
| Temperature Limit | 200 deg F (93.3 deg C) |
| Air Operating D/P Range (at 60 deg F, 14.7 psia) | 0.64 to 28 in W.C. |
| Water Operating D/P Range (at 70 deg F) | 2.31 to 102 in W.C. |
| Velocity Range Not Recommended (vibration) | 53 to 79 ft/s |
| Recommended Upstream (one elbow/tee, in-plane) | 7 diameters |
| Recommended Upstream (all valves) | 24 diameters |
| Recommended Downstream | 5 diameters |
| Head Dimensions | 2-1/16 in (52.40 mm) x 2-1/8 in (53.98 mm) overall head; 3-5/8 in (92.08 mm) approx height |
| Compatibility Range | 6 in to 24 in schedule 40 (Std wt for 24 in) |
| Agency Markings | USA: California Proposition 65 (Lead) |
| Warranty | Dwyer manufacturer warranty |
What’s In the Box
- Dwyer DS-400-8-LV DS-400 Averaging Pitot Flow Sensor (for 8" schedule 40 host pipe, K = 0.675)
- 3/4 in male NPT brass compression fitting (packing gland) - pre-installed
- Stainless steel nameplate with split ring (model and size information)
- Installation and operating instructions (also available below as PDF)
- Note: 3/4 in NPT female thred-o-let or saddle clamp for pipe mounting NOT included - specify separately based on pipe wall thickness and access requirements
Related Products
the with-valves (standard) variant of the same flow sensor — includes integrated brass quarter-turn ball valves on both pressure connections for sensor zeroing isolation.
Other DS-400 flow sensors for adjacent pipe sizes:
For 8 in pipe with standard flow rates and lighter-duty applications, the DS-300 variant is also available at lower cost:
Documentation
Frequently Asked Questions
The DS-400-8-LV is a Series DS-400 averaging Pitot tube flow sensor designed for installation in 8" schedule 40 host pipe. It develops a differential pressure proportional to the square of the flow rate through the pipe — that differential is then read by a Dwyer Magnehelic® (air), Capsuhelic® (liquid), or any other compatible differential pressure gage or transmitter, and converted to flow rate via the Dwyer flow equations using K = 0.675 (the flow coefficient calibrated for the inside diameter of 8" schedule 40 pipe). The sensor itself is built from a 304 stainless steel sensor tube with a brass compression fitting; suitable for water, steam, air, gases, oils, and other compatible fluids.
The sensor is not made from schedule 40 pipe. The sensor body is built from 304 stainless steel (sensor tube) and brass (compression fitting). “Schedule 40” refers to the host piping this sensor is calibrated to drop into — the flow coefficient K = 0.675 is based on the inside diameter of 8" schedule 40 pipe. If you install this sensor into a non-schedule-40 pipe of the same nominal size, the actual inside diameter will be different and the K factor won't be accurate as-published; the formulas in Bulletin F-50 use the actual internal diameter D, so you'd need to recalculate.
Pick the DS-400 for pipe sizes 6 in to 24 in with higher flow rates or applications where the increased forces at higher velocities require the 3/4 in diameter stainless steel construction. The DS-400 uses a larger 3/4 in NPT compression fitting (vs. 1/4 in on DS-300) and supports insertion lengths up to 24 in. Pick the DS-300 (only available up to 10 in) when budget is tight, flow rates are moderate, and the lighter-duty design is acceptable. For overlapping sizes (6 in, 8 in, 10 in), choose based on duty severity.
-LV (less valves) means this sensor ships without the integrated brass quarter-turn ball valves that are standard on the with-valves model. Choose -LV when (1) you'll use an external 3-valve manifold for isolation and zeroing, (2) the application doesn't require in-service gage zeroing, or (3) you have valves on hand to field-install. Order the DS-400-8 (with-valves) instead if you want isolation built into the sensor body for convenient in-place zeroing.
Use the Dwyer flow equations (from Bulletin F-50). For any liquid: Q (GPM) = 5.668 x K x D² x sqrt(ΔP / Sf). For steam or any gas: Q (lb/Hr) = 359.1 x K x D² x sqrt(p x ΔP). For any gas (SCFM): Q (SCFM) = 128.8 x K x D² x sqrt(P x ΔP / ((T+460) x Ss)). Where K = 0.675 for this pipe size, D is the internal pipe diameter in inches, ΔP is the measured differential pressure in inches W.C., and the other terms are media properties (Sf = specific gravity at flow conditions, p = density in lb/ft³, P = static line pressure in psia, T = temperature in deg F, Ss = specific gravity at 60 deg F).
For air at 60 deg F and 14.7 psia (standard conditions), the recommended differential pressure operating range is 0.64 to 28 in W.C. For water at 70 deg F, the recommended D/P range is 2.31 to 102 in W.C. Velocity ranges to avoid (continuous operation in these ranges can cause vibration damage to the sensor): 53 to 79 ft/s. For other gases, liquids, or operating conditions, consult Dwyer for recommended operating ranges.
Dwyer's rule of thumb is 10 to 15 pipe diameters upstream and 5 downstream. Specific minimums depend on what's upstream of the sensor: 7 diameters for one elbow or tee in-plane (9 out-of-plane); 8 diameters for two 90 deg bends in same plane (12 out of plane); 18 diameters for two 90 deg bends in different planes (24 out of plane); 8 diameters for reducers or expanders; and 24 diameters for all valves (partially open). For laboratory or high-accuracy work, add 25% to these values. Control valves should always be located after the flow sensor, never before it.
For air or gas flow: install the sensor in the upper quadrant of the pipe so that any condensate drains back to the pipe (and not into the instrument tubing). For liquid or steam flow: install in the lower quadrant so any air bleeds back to the pipe (and not into the gage). In both orientations, the side connection on the sensor head is high pressure (HP) and should be pointed upstream; the top connection is low pressure (LP). Connect HP to the gage's high port, LP to the gage's low port.
The differential pressure side of any Dwyer (or equivalent third-party) differential pressure gage or transmitter with appropriate range. Standard pairings: Dwyer Magnehelic® for air flow (mechanical D/P gage, multiple ranges); Dwyer Capsuhelic® for liquid flow (rugged mechanical D/P gage rated up to 500 psig line pressure); Dwyer Series 605, 616, or 629 transmitters for electronic 4-20 mA output to a BAS. The Dwyer A-471 Portable Capsuhelic® Gage Kit pairs with the SAE 45 flared adapter ports (included on DS-400 with-valves models; optional on DS-300) for portable flow surveying.
