The gas-purge system transmits the pressure head of water in the stream to the manometer location. A gas is fed through a tube and bubbled freely into the stream
through an orifice at a fixed elevation in the stream. The gas pressure in the tube is equal to the piezometric head on the bubble orifice at any gage height.

The standard bubble rate in the USGS bubbler system is 60 bubbles per minute in a sight glass. This low rate conserves gas supplies and keeps friction in the polyethylen tubing to less than an equivalent 0.01 ft. of water in feed lines as long as 250 feet.

The Conoflow Sight Feed Assembly is the standard regulator to control bubbler system gas flow rates. It consists of a Conoflow differential gas regulator, a sight fed glass, bypass purge tubing and valve assembly. The diaphragm of this regulator acts on a soft-seated plug to admit just enough gas to maintain a pressure drop of 1.5PSI across the needle valve. This ensures a Constant gas flow rate even under changing water levels (pressures).

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Nitrogen Tank Regulator Assembly-Model 9105

Is a standard gas tank regulator for the nitrogen supply tank. It is necessary to reduce the 3000 PSI tank pressure to 60 PSI for theConoflow sightfeed assembly supply pressure.

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Orifice Tubing-Model 9324
The orifice line tubing is a special heavy wail black polyethylene line, 3/8" OD x 1/8" ID designed for bubble-orifice installations.

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The proper placement of the orifice is essential for an accurate stage record. The orifice should be located where the height of water above it represents the stage in the river. If it is partly buried in sand or mud, the recorded stage will be greater than that in the river. An orifice preferably should not be installed in swift cutrents. If this is unavoidable, it must be kept at right angles to the direction of flow. A recommended mounting for swift-flow conditions is for the orifice to be mounted flush with the wall of the mounting structure. Care should also be taken to keep the orifice out of highly turbulent flow.
 
 
 
 
 

HS-23 Dry Bubble Unit

The Model HS-23 Dry Bubble Unit is a gas purge system which provides a constant differential pressure (3-5 psi) above the pressure head at the end gas tube or bubbler. This constant differential pressure maintains a constant bubble rate through the gas tube and enables the Aquagage 9100 orUSGS PS-2 pressure sensing instrument to measure the change in pressure head and thereby the depth of river or stream. The HS-23 is a new design which incorporates a vernier scale regulator valve for setting the bubble rate.

The unit is precalibrated so that a bubble rate can beaccurately set in the field without the need for furthercalibration. This design eliminates the need of sight glass and oil reservoir for the setting of the bubble rate. It is a low maintenance unit with minimum components ensuring increased reliability.

The HS-23 can be set up as either a Double or Single Line Gas Purge System.
Single Line Gas Purging System: the HS-23 and the pressure sensing instrument, can be located up to 500 feet (150 m) from the stream.

Dual Line Gas Purge System: the HS-23 and the pressure sensing instrument are located more than 500 feet (150 in) from the stream. This set up eliminates long lag times in sensing pressure changes caused by friction in the gas line.

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USGS Model 9330-Standard Orifice Static Tube

(SOST) is a modification of the standard orifice and is designed to reduce drawdown where water velocities reach 3 ft/s or greater.

The alignment of the SOST assembly is set at the time of fabrication and should not be altered. The SOST assembly vent hole must be positioned below the minimum water level. The assembly can be installed at any angle from vertical to less than horizontal. However, if the SOST assembly is not in the vertical position, it must be perpendicular to the flow streamline (that is, not pointing upstream or downstream) . The SOST assembly must not be installed in the horizontal position.