Issue Date: August 30, 2007

Revision Date:  June 27, 2011

Western Fiberglass, Inc.

Co-Flow Hydraulic Interstitial Monitoring System
Propylene Glycol Filled Pressurized Interstitial Space


Certified as a continuous, liquid-filled interstitial space leak detection system for use only with Western Fiberglass, Inc., double-walled/coaxial flexible pipelines.
Maximum length is 200 feet.
No restrictions on pipeline diameter.

Operating Principle:
Similar to the methodology that has been applied to liquid-filled interstitial double-walled tanks.
A pressurized reservoir is attached to the piping interstice and filled with propylene glycol.
A pressurized cylinder is used to maintain pressure in the reservoir. Pressure is normally adjusted to 50 psig for a typical service station.  The cylinder contains nitrogen or air and a pressure switch to monitor pressure in the reservoir (low pressure alarm is typically set at 35 psig).
The reservoir contains a dual-point level sensor that monitors the liquid level and provides an alarm if the liquid level is either too high (ingress of liquid) or too low (egress of liquid).
Once the liquid leaks out of the system, the leak becomes an air leak.  Pressure drops are rapid and a pressure loss alarm is produced.
The method must be used with a dual-point sensor system that will properly fit into the reservoir, is compatible with the interstitial liquid, and is on the NWGLDE list.
Sensors can be used to shut down the turbine system and/or alert the operator that a potential problem exists.

Alarm Conditions:

Average Liquid Level Required to Alarm*


Time to Alarm in Hours, as a Function of Leak Rate

Lower Level Alarm (in)

High Level Alarm (in)


Leak Rate (gph)

For 3 inch Dia Reservoir (hours)





















*The liquid level required to alarm is controlled by the level of liquid in the reservoir.  This level is determined by the operator when filling the reservoir.  The reservoir is filled to a level where the dual point sensor is floating midway between the low and high level alarm.
Previously conducted theoretical calculations and laboratory measurements confirm that dilution of the propylene glycol used in the interstice of the WFG system will produce a significant reduction in the alarm time.  The use of diluted propylene glycol (from100% to 50%) will reduce the alarm time by a factor of approximately 7.2.  For example, an alarm time of 80 minutes would be reduced to around 11 minutes.


Western Fiberglass, Inc. underground double-walled/coaxial flexible pipelines containing gasoline, gasohol, diesel, heating oil #2, kerosene, aviation fuel, or motor oil.

Equipment requires no calibration other than to ensure the reservoir is at a level where the dual point sensor is floating midway between the low and high level alarm.
The electronics must be calibrated and maintained in accordance with the sensor/monitoring equipment instructions.

Pipeline fittings with interstitial communication tubing must only be located in sumps or pump pits – direct burial is not permitted.  The interstice must be filled from the low point in the pipeline to minimize trapped air.
The evaluation was conducted in a Western Fiberglass, Inc. double-walled/coaxial flexible pipeline with an interstitial capacity of 1.64 gallons, an inside diameter of 1.5 inches, and a length of 200 feet.
Installers must be certified by both the piping and sensor manufacturer.
The testing was conducted on the “new” double-walled/coaxial flexible pipe (manufactured beginning March, 2006).  It can be used in place of the “old” double-walled/coaxial flexible pipe where the pressure is near ambient.
Evaluation was conducted with an interstitial pressure of 50 psig.

Western Fiberglass, Inc. Evaluator:  Ken Wilcox Associates
1555 Copperhill Parkway Tel:  (816) 443-2494
Santa Rosa, CA  95403 Date of Evaluation:  02/23/07
Tel:  (707) 523-2050  


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Equipment should be installed and operated in accordance with all applicable laws and regulations.  For full details, please refer to our expanded "DISCLAIMER" page.