Despite electronic control systems and measurement instrumentation dominating applications in the processing and manufacturing industries, pressure, temperature, level, flow measurement and calibration technology company Wika argues that mechanical measurement instrumentation remains relevant and important in South African industries.

Although electronic and mechanical flow meters achieve the same measurement objective, primary flow elements can be used for applications where electricity supply is not available. Primary flow elements are less prone to failure owing to no moving parts, in comparison to other mechanical flow meters, says Wika product specialist Sagadevan Kanniappen.

“There is often debate regarding which flow measurement technology is superior. However the consensus is that both mechanical and electronic flow measurement are required in industry. What is important is that customers are informed of which technology is best suited to their application.”

Primary flow elements are used in a variety of process applications, which are found in numerous industries, such as power generation, oil and gas, petrochemicals and chemicals, water, pulp and paper, to name a few.

Although the technology is not new, primary flow elements remain indispensable and are becoming more sought-after in countries such as South Africa, where there is an energy shortage and continuous power-cuts can suspend operations. “Having mechanical instrumentation can allow certain processes to operate manually, until power is restored.”

“Wika also provide a completely mechanical option for users who require an assembly purely for local indication purposes when transmission of an output signal to a supervisory system or controller is not required. “Wika offers a differential pressure (DP) gauge with a square-root incremented dial, fitted to a valve manifold, which, in turn, is fitted to the pressure tappings across the primary flow element,” adds Kanniappen.

Users also have the option to include a variety of accessories, all manufactured by Wika, such as diaphragm seals and flushing rings, which can be used to prevent blockage of the pressure tappings during casual operation when primary flow elements are used on lines containing highly viscous or particle-laden media.

Kanniappen says these elements provide a longer installed life span, as they are less prone to process and environmental wear, provided the correct element and material of construction is selected for the application.

During operation, the upstream and downstream pressure is measured using a DP gauge or transmitter across the primary flow element by means of pressure-tapping points.

The flow rate in the line is proportional to the square root of the DP across the primary flow element.

When using DP flow, if the user suspects electronic component damage, owing to power surges or irregular behaviour of the process, the user can be assured that the damage, if any, will be at the DP transmitter.

If the transmitter has to be replaced, the primary flow element does not need to be removed from the line. This keeps downtime, which is costly, to a minimum, he adds.

“We conduct ongoing research and development to provide the industry with innovative flow measurement technology. Currently, the high-head recovery series of primary flow elements offered by Wika introduces a new dimension to DP flow measurement.”

The series requires no minimum upstream or downstream straight runs, which is mandatory with most flowmeters, while providing the highest-pressure recovery and, in turn, the lowest permanent pressure loss in the class of primary flow elements, adds Kanniappen.

“The Propak model of the HHR series is the premium option from our portfolio of primary flow elements, and is suitable for custody transfer applications in the oil and gas industry and is compliant with the American Petroleum Institute 22.2 test protocol.”

At Wika, every primary flow element is uniquely sized to suit the specific process data for a pipeline, header or duct. This affords design engineers the flexibility to specify the maximum amount of permanent pressure loss owing to the primary flow element that can be tolerated for a specific line.

“This is a desirable factor for many engineers, as increased permanent pressure losses in a line will result in decreased efficiency and increased operating costs,” he adds.

As a result, using the correct primary flow element will provide a lower cost of ownership over a period, when compared to other flow measurement methods.

All Wika primary flow elements are designed in accordance with the principles and requirements of international standards, such as the International Organisation for Standardisation 5167 (ISO 5167) standard. There are many other international standards and guidelines in addition to the ISO 5167 standard that Wika primary flow element designs comply with, concludes Kanniappen.