Series 1221/1222/1223 Flex-Tube® U-Tube Manometer

These inexpensive manometers measure positive, negative and differential pressures. Dwyer® Flex-Tube® U-Tube Manometers combine the inherent accuracy of the simple "U" Tube with the durability of tough, long-lasting plastic construction. Columns are of .375" O.D. flexible and shatter proof clear butyrate tubing. They are easily accessible for cleaning. Indicating tube is backed by white scale channel to provide maximum color contrast. Scales are extruded high impact polystyrene plastic, formed to hold columns in perfect alignment. Stark white scales have graduations and numbers silkscreen-printed in black for maximum legibility.

You can choose from numerous models and features including over-pressure safety traps, in full scale ranges from 8" to 36" of water or mercury. All are suitable for total pressures to 100 psi - for determining velocity and static pressures, leakage, fan and blower efficiency, filter resistance, and gas pressures. Ideal wherever a portable, direct reading manometer is needed. Standard ranges and markings as shown, or special ranges, colors, logos and brand names for OEM quantity orders are available.

Click here, if you require a Material Safety Data Sheet for the Fluoroscein Green Concentrate or the Red Gage Fluid.

Models & Ordering

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Model Number Description Usually Ships Price Order
1221-12-W/M U-tube manometer, range 6-0-6" w.c., 7.9 oz (225.5 g) mercury required to fill. Same Day $32.00 Order
1221-16-W/M U-tube manometer, range 8-0-8" w.c., 9.5 oz (269 g) mercury required to fill. Same Day $33.25 Order
1221-20-W/M U-tube manometer, range 10-0-10" w.c., 11.1 oz (314.5 g) mercury required to fill. Same Day $35.00 Order
1221-24-W/M U-tube manometer, range 12-0-12" w.c., 13.4 oz (379.7 g) mercury required to fill. Same Day $36.75 Order
1221-36-W/M U-tube manometer, range 18-0-18" w.c., 17.3 oz (491.1 g) mercury required to fill. Same Day $41.00 Order
1221-8-W/M U-tube manometer, range 4-0-4" w.c., 6.3 oz (178.5 g) mercury required to fill. Same Day $29.25 Order

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  • Minor Divisions of 1/10" water column (or 2mm water column on metric units) are silkscreened in jet black on stark white scale for positive definition. Easy to read, even at a distance, they are acrylic coated for permanence. All models are furnished with one 3/4 ounce bottle of fluorescein green color concentrate with special wetting agent for W/M models, or 3/4 ounce bottle of red gage fluid for "D" units.
  • Series 1221 Manometer - Our simplest, lowest cost basic U-gage. A dependable U-tube manometer that withstands hard use and provides accurate, high visibility readings. For use with water, mercury or red gage fluid. For mercury filled manometers, a scale clamp bar, Dwyer® Part No. A-363 (available as an extra for Series 1221 - and standard on Series 1222) is recommended. One pair of carrying plugs and a pair of non-kink vinyl tube connectors are included with each manometer.
  • Series 1222 Manometer - All the features of the 1221 plus magnetic clips for mounting to any vertical steel surface, and clamp bar to insure against U-tube slipping. (Especially recommended for manometers used with mercury.) Both magnets are easily removed and replaced at the user's convenience.
  • Series 1223 Manometer - Our finest U-gage - for either portable or stationary use. Safety traps prevent loss of indicating fluid in case of accidental over-pressure. Tubing is permanently bonded to a molded, high impact acrylic plastic top that contains safety traps. Large magnetic clips and clamp bar are provided. Standard type "a" connections include two rapid shut-off type molded nylon tubing connections, two 3' lengths of flexible Tygon® plastic tubing, and two 1/8" pipe thread to tube adapters.


Model Number Description Usually Ships Price Code Order
A-101 1 oz dispenser bottle of red gage fluid, .826 sp. gr. Same Day $6.80 Order
A-102 4 oz bottle of red gage fluid, .826 sp. gr. Same Day $13.00 Order
A-103 1 pt bottle of red gage fluid, .826 sp. gr. Same Day $30.25 Order
A-104 1 qt bottle of red gage fluid, .826 sp. gr. Same Day $54.50 Order
A-126 1 oz dispenser bottle fluorescein green color concentrate. Same Day $9.90 Order
A-220 Clear flexible vinyl tubing is easily inspected, and is therefore best for test applications where a possibility of fluid entering the tubing exists. 3/16" ID x 5/16" OD, lengths to 500'; 45 psi maximum pressure @ 73°F. Same Day $0.25 N Order
A-319 Flexible red PVC connector, 3/16" ID rubber tubing to 1/4" ID plastic tube for 1221,1222 and 1227 manometers. Same Day $3.40 Order
A-339 Adapter, brass, 1/8" NPT to 3/16" rubber and 1/8" ID plastic tubing. Same Day $3.90 Order
A-363 Scale clamp bar for 1221 manometer. Same Day $5.10 Order
A-364 Magnet assembly for 1222 manometers, 2 required (3 required for 1222-36 and M-1000). Same Day $7.20 Order

Model Chart

EXAMPLE 1221 8 W/M AT Series 1221-8-W/M-AT U-Tube Manometer, range 4-0-4" w.c. using water/mercury, with aluminum tag.
      U-Tube Manometer
U-Tube Manometer
U-Tube Manometer
    4-0-4" w.c.
6-0-6" w.c.
8-0-8" w.c.
10-0-10" w.c.
12-0-12" w.c.
18-0-18" w.c.
100-0-100 mm w.c.
150-0-150 mm w.c.
200-0-200 mm w.c.
300-0-300 mm w.c.
500-0-500 mm w.c.
1000-0-1000 Pa
1500-0-1500 Pa
2000-0-2000 Pa
2500-0-2500 Pa
3000-0-3000 Pa
4500-0-4500 Pa
  Inches of Water/Mercury
Inches of Water Using Red Gage Fluid
Aluminum Tag
NIST Certificate of Calibration
Type B Connections (available with 1223 only)
Type C Connections (available with 1223 only)
Type D Connections (available with 1223 only)
Type E Connections (available with 1223 only)

Product Literature


Catalog Pages




What are the principle advantages of red gage fluid over water for use in manometers?
Red gage fluid is slow to evaporate, won't freeze, is more readable and produces slightly expanded scales for better reading resolution.
Is routine maintenance required for a Dwyer red gage fluid type manometer?
Yes. The zero point should be checked periodically as well as the fluid level. After a year of service, particularly with dirty air, the fluid should be replaced to assure that specific gravity changes are not affecting the accuracy of the reading.
Will the water manometers freeze?
Yes, if the temperature drops below 32 degrees Fahrenheit, the fluid in the manometer will freeze. The fluid used in "W/M" style manometers is water-based with a small amount of fluorescent green fluid to enhance the meniscus. The other gage fluids have a lower freezing point, however, it is recommended that the manometers be stored above 32 degrees Fahrenheit.
Since water will not mix with oil, why can't a D-style manometer be used to measure water pressures?
The weight of the water itself is also being measured which results in erroneous readings.
Why doesn't 1 inch on the scale of a 1223-12-D manometer equal 1 inch on a ruler?
The calibration scale on the manometer has been compensated for the specific gravity of red gage fluid which is less than water.

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