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A King downpipe is the simplest type of liquid level sensor, often referred to as a “bubbler." This is merely a length of open ended pipe that extends downward into the tank. LiquiSeal™ or Purge Control differential pressure air flow regulators are highly refined versions of the basic bubbler air control.
Continuous Level Measurement
Simple Proven Sensing Technique
Suitable for Corrosive or Aggressive Liquids
Simple Proven Sensing Technique
Suitable for Corrosive or Aggressive Liquids
When purged with compressed air, liquid within the downpipe is displaced by air pressure equal to the hydrostatic force of liquid in the tank. If carefully regulated at a low rate of flow, air pressure will constantly maintain equilibrium against the force of the liquid. Air escapes out through the bottom of the pipe unless needed to increase pressure as liquid force (depth) increases.
788 D/P Purge Control is a differential pressure regulator and air flow control. It generates a constant flow of compressed air to purge a downpipe. Its integral differential pressure transmitter provides 4-20 mAdc output proportional to liquid level.
The primary sensor element is typically 3/4 in. diameter pipe purchased from a local source. Always select piping material for compatibility with the tank contents. Downpipe purge systems can be used to measure virtually any type of liquid product including resins, asphalt or corrosive materials.
Output is proportional to liquid depth and can be transmitted as an electronic 4-20 mA signal or pneumatically as a direct 1:1 pressure signal.
LiquiSeal D/P purge control is a fully integrated air purge regulator and level transmitter. Operation is based on the control regulating a continuous 1 cfh (cubic foot per hour) flow of compressed air into the tank downpipe. An internal differential pressure sensor element converts resulting pressure into a 4-20 mA dc two wire signal.
788 D/P Purge Control is a more basic differential pressure regulator and air flow control. It generates a constant flow of compressed air to purge a downpipe. Its integral differential pressure transmitter provides 4-20 mAdc output proportional to liquid level. 780 Purge Control is an all-pneumatic version that does not include the integral transmitter. It provides a 1:1 pressure signal to a compatible indicator or external transducer through 1/4 in. airline tubing. The purge control holds a fixed pressure differential across a precision orifice to ensure constant flow rate of 1 cfh (cubic foot per hour). This regulated low flow rate makes it possible to maintain a linear 1:1 response of the sensing system. In this way, back pressure sensed is equivalent to the hydrostatic head pressure due to actual liquid depth.
Pneumatic Output Signal
Purge Control or LiquiSeal Control provides air pressure signal to an external transmitter or compatible indicator (with integral transducer). Typically, 1/4” poly or soft copper tubing is used to convey the pressure signal up to 1000 feet from the tank.
Electronic 4-20 mA Output
D/P Purge Control or D/P LiquiSeal transmitter provides a 4-20 mA output over a two wire cable to an indicator or the analog I/O of a PLC. Using twisted pair shielded cabling permits transmission distances of several thousand feet to a remote receiver.
Hazardous Zone Service - The downpipe sensor and pneumatic components are fully compatible with explosion hazard environments. This makes pneumatic the sensible alternative for hazardous areas without the cost and complications of intrinsic safety barriers or explosion-proof products.*
Transmitter turndown ratio is 3:1 for the 0–15, 0–30, 0–50 psid nominal ranges.
Nominal Minimum Range of Adjustment
0–5 psid 0–3 psid 0–83 in. thru 0–138 in. water / 0–2.1 m thru 0–3.5 m water
0–10 psid 0–3 psid 0–83 in. thru 0–277 in. water / 0–2.1 m thru 0–7.0 m water
0–15 psid 0–3 psid 0–83 in. thru 0–415 in. water / 0–2.1 m thru 0–10.5 m water
0–30 psid 0–10 psid 0–277 in. thru 0–830 in. water / 0–7.0 m thru 0–21.0 m water
0–50 psid 0–15 psid 0–415 in. thru 0–1384 in. water / 0–10.5 m thru 0–35.1 m water
IMPORTANT! Accuracy, linearity, and non-repeatability values are based on nominal range.
Call Flow Factor for more information - 866-360-9830
or email info@flowfactor.com
or visit our contact page on the web site.
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