Why Measuring Differential Pressure Across a Filter or Strainer is Important

Differential pressure gauge.
(Ashcroft)

In many applications fluids passing through a pipe require filtering this results in the need for continuous differential pressure monitoring. Differential pressure gauges, switches and transmitters help monitor your processes.

Filters and strainers commonly are positioned to capture solids and particulates. The filter will obstruct the flow through the pipe lowering the pressure on the downstream side. These effects may vary depending on the filters construction. Filter media is the material that removes impurities. The smaller the pores, the larger the friction. Higher friction means greater pressure drop. Contaminants or particulates that build up in the filter will reduce media flow. As the filter becomes clogged, the downstream pressure drops. This results in an increased differential pressure, also referred to as the Delta-P. Saturated filters may also begin to shed

Differential pressure switch.
(Ashcroft)

captured particles. With the filter no longer functioning properly, the contaminants can escape into the process. This is why proper monitoring of pressure drop is crucial.

Differential pressure transmitter.
(Ashcroft)

Differential pressure is measured by placing taps both before and after the filter. A differential pressure measuring instrument can be connected to detect the high side and low-side pressures. The instrument will report the difference between the two sides. The saturation point will be indicated when the Delta P value reaches a predetermined threshold. This value was derived from a calculation that factors in the flow rate fluid viscosity and filter characteristics. The filter manufacturer can be contacted for help in identifying the optimum differential pressure value that tells you when it'stime to service the filter.

When specifying a differential pressure instrument there are two important factors to consider. The first is the DP range, which is based upon the most difference in pressure that the restriction is likely to produce. The second is the instruments ability to contain the static pressure, which is simply the pressure in the line while the differential pressure remains the same. A higher line pressure may require an instrument rated for higher static pressure.

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NACE Standards - Measuring the Pressure of Sour Gas and Crude

In 1943 a group of corrosion engineers working in the pipeline industry formed the National Association of Corrosion Engineers with the goal of "protecting people, assets, and the environment from corrosion”. In the 1960s, they commenced development of control standards to define appropriate materials for a wide variety of corrosive applications, including oil and gas production and refinery facilities. In 1993, the organization was renamed “NACE International”.

Today, NACE offers over 150 standards that address metal corrosion in a vast number of applications ranging from exposed metal structures to corrosion resistant coatings on railroad cars.

The following NACE Measuring Pressure of Sour Gas and Crude White Paper (courtesy of Ashcroft) discusses NACE standards that specifically address corrosion resulting from expo- sure to sour gas or sour crude.

You can download the entire NACE Standards Sour Gas and Crude White Paper here, or review it in the embedded document below.

For more information, contact Mead O'Brien at (800) 892-2769 or visit their web site at https://meadobrien.com.

NACE Standards - Measuring the Pressure of Sour Gas and Crude from Mead O'Brien, Inc.

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Saturated Steam Table

A saturated steam table shows temperatures and pressures for water at the liquid/vapor transition (i.e. points lying along the liquid/vapor interface shown in a phase change diagram), as well as enthalpy values for the water and steam under those conditions. The sensible heat of water is the amount of thermal energy per pound necessary to raise water’s temperature from the freezing point to the boiling point. The latent heat of vapor is the amount of energy per pound necessary to convert water (liquid) into steam (vapor). The total heat is the enthalpy of steam (thermal energy per pound) between the listed condition in the table and the freezing temperature of water.

By definition a saturated steam table does not describe steam at temperatures greater than the boiling point. For such purposes, a superheated steam table is necessary.

Mead O'Brien
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Saturated Steam Table

Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

Data for this saturated steam table was taken from Thermal Properties of Saturated and Superheated Steam by Lionel Marks and Harvey Davis, published in 1920 by Longmans, Green, and Company.

Triple Offset Butterfly Valve Operation and Features

Triple offset butterfly valves provide superior performance, increased durability, reliability and lower ownership cost than traditional valves.

Triple offset butterfly valves are recognized for excellent flow control characteristics, zero leakage, and reliability. They are designed for superior performance in high pressure and extreme temperature applications. Their design includes metal seats which are inherently fire safe. They maintain their zero leakage seal even in extreme operating conditions. Finally, triple offset butterfly valves typically weigh less than similar sized valves, allowing for easier installation and maintenance.

TRICENTRIC^®, the leading manufacturer of triple offset valves, engineer their products to meet stringent industry requirements and offer cost savings to the end user through improved life cycle costs, reducing emissions, reducing downtime and requiring lower maintenance costs.

Triple offset butterfly valves have a huge installed base and a commonly used in a range of industries including:

• Aerospace
• Conventional power 
• Nuclear power
• Oil & gas / refining
• Desalination
• Chemical processing 
• Pulp & paper mills
• Military

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(800) 892-2769

Hot Water for Industry from Mead O'Brien

Mead O'Brien, in partnership with Armstrong International, delivers accuracy, simplicity and unparalleled performance in instantaneous hot water generation, distribution and precision temperature control.

From a single product, to a complete fully integrated system, Mead O'Brien can provide a hot water solution to meet your most demanding needs.

Products include standard and application-customized steam/water instantaneous water heaters for any process application requiring very specific temperatures, from chilled water to temperatures as high as 212°F (100°C), as well as Mixing Centers, VFD Pump Assemblies, Hot & Cold Water Hose Stations, Gas-Fired Water Heaters, and Digital Control Valves.

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(800) 892-2769

Industrial Thermowells: Sometimes Taken for Granted, but Critically Important

Thermowells come in a wide variety
of shapes, materials, and sizes.
(Courtesy of Ashcroft)

One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as a thermowell. This may be thought of as a thermally conductive protrusion into a process vessel or pipe allowing a temperature-sensitive instrument to detect process temperature without opening a hole in the vessel or pipe.

Thermowells are critically important for installations where the temperature element (RTD, thermocouple, etc.) must be replaceable without de-pressurizing the process.

Thermowells may be made out of any material that is thermally conductive, pressure-tight, and not chemically reactive with the process. Most thermowells are formed out of either metal (stainless steel or other alloy) or ceramic materials.

A simple diagram showing a thermowell in use with a temperature sensor (RTD) is shown here:

Typical RTD thermowell installation.

As useful as thermowells are, they are not without their caveats. All thermowells, no matter how well they may be installed, increase the first-order time lag of the temperature sensor by virtue of their mass and specific heat value. It should be intuitively obvious that a few pounds of metal will not heat up and cool down as fast as a few ounces’ worth of RTD or thermocouple, and therefore the addition of a thermowell to the sensing element will decrease the responsiveness of any temperature- sensing element. What is not so obvious is that such time lags, if severe enough, may compromise the stability of feedback control. A control system receiving a “delayed” temperature measurement will not see the live temperature of the process in real time due to this lag.

For more information on thermowells, contact Mead O'Brien by visiting https://meadobrien.com or by calling (800) 892-2769.