Validating the Hysteresis of Pressure Switches on Pipeline Pigging Systems

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A pipeline integrity services company needed to accurately test the hysteresis1 of the pressure switches used to control their pigging systems. We will show how using a Druck DPI 802 pressure indicator/loop calibrator is an improvment over previous testing methods and pipeline testing equipment.


This company offers a variety of services to assist oil and gas companies assess the condition of their pipelines. These pigging systems are sent into the pipeline and are used to generate in-depth knowledge of the pipeline condition, including cracks and damage.

It is essential that the pig be in good working order before entering the pipeline. If the pig fails, the pipeline is rendered unusable until the pig is removed. Therefore, the company sends a field technician to the site to perform a thorough test/calibration check on the entire system before it is used.

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An integral part of the pigging systems is a pressure switch that, unless energized, will not allow the pig to operate. Tests revealed that if the hysteresis of this switch is checked, it is possible to determine if the switch will fail when in operation.

Previously, technicians used a mechanical hand pump and gauge to measure the trigger point for the pressure switch. Since the gauge had to be manually read, the measurement results were inaccurate and inconsistent due to human error.
1 The influence of the previous history or treatment
of a body on its subsequent response to a given
force or changed condition.







The pipeline integrity services company includes the DPI 802 Druck Pressure Indicator/Loop Calibrator as part of a test box that consists of equipment to check/calibrate the pigging system.

As part of the test/calibration check, the technician connects the DPI 802 to the pressures switch similarly to that shown in Figure 3, below.pipeline testing equipment

When in the switch test mode, the DPI 802 identifies (to 0.01 of a psig) the actual switch point and reset switch point (usually between 45 to 50 psigl. If the switch operates out of this set band, it indicates the diaphragm of the switch is damaged and may fail. To avoid the possibility of failure, the switch is replaced.


pipeline testing equipmentThe DPI 802 has a built-in software routine/task specially designed to test pressure switches. Once connected to the switch and pressure is applied via the hand pump, the DPI 802 precisely measures and displays the trigger point for the switch. Technicians can then use this data to make an accurate assessment of the reliability of the pressure switch before it is sent into the pipeline, which means the pipeline is not shut down any longer than necessary.

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Measurements were taken with 0 to 20 bar DPI 802 Druck Pressure Indicator/Loop Calibrator unit.

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