Showing posts with label Ashcroft. Show all posts
Showing posts with label Ashcroft. Show all posts

Sunday, September 30, 2018

Industrial Thermowells: Sometimes Taken for Granted, but Critically Important

Ashcroft Thermowells
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:
thermowell installation
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.

Thursday, September 27, 2018

Five Important Criteria in Applying Pressure Gauges

Ashcroft pressure gauge
Process pressure gauge.
(Ashcroft)
Pressure gauges are installed in countless industrial and commercial applications around the world. From hygienic pharmaceutical process lines, to the most unpleasant and hostile areas in chemical, power, and food processing plants.

While there are millions of possible combinations of shapes, sizes, options and materials, pressure gauges all share the five  following application criteria, required for safe use and long product life.
Ashcroft diaphragm seal
Diaphragm seal.
(Ashcroft)


1 - Process Media Properties: Media that is corrosive, sludgy, or that can solidify is a potential problem for pressure gauges. In non-corrosive, non-clogging media applications, a direct connection without intermediate protection can be applied. For process media that could potentially clog or chemically affect the gauge's wetted parts, a diaphragm seal should be used.

2 - Process Media Temperature: Very hot media, such as steam or hot water, can elevate the gauge's internal temperature leading to failure or an unsafe condition. For high temperature applications, the use of a "pigtail siphon" or diaphragm seal is recommended. Siphons act as a heat sink and lower the exposure temperature. Diaphragm seals isolate the gauge from the higher temperatures.

Siphon
Pigtail siphon.
3 - Ambient Operating Temperature and Environment: It is important to know the ambient environmental rating for any process instrument. Elevated ambient temperatures, moisture, vibration, and corrosive atmospheres can all affect accuracy, calibration, and safety. Choose the proper housing and mechanism materials if oxidizing or reducing atmospheres exist, and consider the addition of ancillary devices, such as remote diaphragm seals to physically relocate the gauge away from the hostile area.

Snubber
Snubber
4 - Severe Pressure Fluctuations: In applications where dramatic line pulsations or strong over-pressure conditions are a possibility, the use of pressure restrictors, snubbers, or liquid-filled gauges will extend the service life of the pressure gauge.

5 - Mounting: Pressure gauges are standardly available with bottom (radial) and back connections. NPT (National Pipe Thread Taper) threaded connections are generally the standard. Many other process connections are available though, such as straight threads, metric threads, and specialized fittings. Make sure you know how the gauge is being connected. When mounting, pressure gauges should be almost always be mounted upright.

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

Friday, August 31, 2018

Industrial Boiler and Burner Limit Control Switches

Ashcroft Limit Control Switch
Ashcroft Limit Control Switch
Designers and manufacturers of industrial boilers are focused on meeting regulatory and safety requirements when developing highly efficient burner management systems (BMS). BMS are responsible for startup, operation and shutdown of a burner boiler systems. BMS monitor temperature, pressure and flow and employs safety shutoffs to shut down the burner boiler if an unsafe condition occurs.

The following white paper describes safety standards for boilers and burners relating to pressure switches and controls.


Wednesday, May 9, 2018

Ashcroft Materials Compatibility and Corrosion Guide

Ashcroft products
Ashcroft products.
Below is a very good materials compatibility and corrosion guide courtesy of Ashcroft.

The reference is intended to serve solely as a general guide in the recommendation of materials for corrosive services and must be regarded as indicative only and not as any guarantee for a specific service.  There are many conditions which cannot be covered by a simple tabulation such as this, which is based on uncontaminated chemicals, not mixtures.

Many of the chemicals listed are dangerous or toxic.  No material recommendation should be made when there is insufficient information, a high degree of risk, or an extremely dangerous chemical.  The end user is responsible for testing materials in his own application, or for securing the services of a qualified engineer to recommend materials.

The end user is responsible for the choice of product(s) in his own application, based upon his own determination of the materials, chemical, and corrosion factors involved. THIS GUIDE AND ITS CONTENT ARE PROVIDED ON AN “AS IS" BASIS WITHOUT WARRANTY OF ANY KIND.

You can refer to the embedded document below, or you can download your Ashcroft Corrosion Guide PDF from this link.

Saturday, March 17, 2018

What Are Isolation Rings?

Isolation Rings
Isolation Rings (Ashcroft)
Isolation Rings are used for protection of sensitive and expensive pressure instrumentation, such as pressure switches, transmitters, and transducers. They isolate the instrument from an aggressive or viscous process. The Isolation Ring is mounted inline with process piping and fits between the process line pipe flanges, similar to wafer butterfly valves.

The ring design includes ring has a  flexible inner cylinder that prevents process media from collecting in the instrument, and therefore assuring reliable and continuous pressure measurement. An integrated needle valve allows for fast and easy removal for instrument repair, replacement, or calibration without interrupting the process media flow. The needle valve can also be used for pulsation dampening.

Watch the video below for a more in-depth understanding of how Isolation Rings are installed and operate.

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

Monday, September 11, 2017

How to Use the Ashcroft 1305 Deadweight Tester

Ashcroft 1305 deadweight tester
The Ashcroft 1305 deadweight tester provide a precise means for generating pressure with high accuracy that can be used as a primary calibration standard. The unit's built-in shuttle valve provides the means to control the rate of pressure increase, while precision adjustment is accomplished with an integral micro vernier displacement valve. 

This video below provides an overview of how to use the the Ashcroft 1305.

For more information on Ashcroft products, contact Mead O'Brien at (800) 892-2769 or visit http://www.meadobrien.com.


Monday, May 8, 2017

Industrial Pressure Switches

Industrial Pressure Switch
Industrial Pressure Switch (Ashcroft)
A pressure switch is a device that detects the presence of fluid pressure. Pressure switches use a variety of sensing elements such as diaphragms, bellows, bourdon tubes, or pistons. The movement of these sensors, caused by pressure fluctuation, is transferred to a set of electrical contacts to open or close a circuit.

Normal status of a switch is the resting state with stimulation. A pressure switch will be in its “normal” status when it senses low or minimum pressure. For a pressure switch, “normal” status is any fluid pressure below the trip threshold of the switch.

One of the earliest and most common designs of pressure switch was the bourdon tube pressure sensor with mercury switch. When pressure is applied, the bourdon tube flex's enough to tilt the glass bulb of the mercury switch so that the mercury flows over the electrical contacts, thus completing the circuit. the glass bulb tilts far enough to cause the mercury to fall against a pair of electrodes, thus completing an electrical circuit. Many of these pressure switches were sold on steam boilers. While they became a de facto standard, they were sensitive to vibration and breakage of the mercury bulb.
Pressure Switch Symbols
Pressure Switch Symbols

Pressure switches using micro type electrical switches and force-balanced pressure sensors is another common design.  The force provided by the pressure-sensing element against a mechanical spring is balanced until one overcomes the other. The tension on the spring may be adjusted to set the tripping point, thus providing an adjustable setpoint.

One of the criteria of any pressure switch is the deadband or (reset pressure differential). This setting determines the amount of pressure change required to re-set the switch to its normal state after it has tripped.  The “differential” pressure of a pressure switch should not to be confused with differential pressure switch, which actually measures the difference in pressure between two separate pressure ports.

When selecting pressure switches you must consider the electrical requirements (volts, amps, AC or DC), the area classification (hazardous, non-hazardous, general purpose, water-tight), pressure sensing range, body materials that will be exposed to ambient contaminants, and wetted materials (parts that are exposed to the process media).

Thursday, January 19, 2017

Dampening the Effects of Vibration on Industrial Pressure Gauges

Pressure gauge
Vibration must be considered
when applying pressure gauges.
Pressure gauges rely on precise and responsive mechanisms to display changes in system pressure as rotational needle movement. By their very nature, these mechanisms are responsive to pulsations within the pressurized system and vibrations that may be evident in the connected piping and structures. The effect of vibration and pulsation is seen as an indicating pointer oscillating rapidly, making a definitive or even useful reading impossible. One solution, applied traditionally, was to fill the gauge with a viscous liquid that would dampen the rapid oscillation of the indicating needle.

While a liquid filled gauge does solve the oscillation problem, it does have a drawback. The liquid in the gauge presents its own set of operational issues requiring consideration in any application.

Provision should be made to check and maintain the liquid level in the gauge
A liquid filled gauge is an additional source of potential leakage in a facility

Ashcroft, a globally recognized manufacturer of gauges for commercial, industrial, and laboratory use, offers a different solution that provides the deflection dampening of a liquid gauge without liquid fill. Available on many of their gauges, the "Plus" option enables stable gauge face display in a dry gauge.

The video below provides a side by side demonstration of a liquid filled and a Plus gauge, so you can see the performance of both types. Share your process gauge requirements and challenges with instrumentation experts, combining your process knowledge with their product application expertise to develop effective solutions.

Thursday, September 29, 2016

Understanding Differential Pressure or Delta-P

differential pressure
Differential pressure or Delta-P
Commonly, filters and strainers are positioned to capture solids and particulate. 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 for particulates that buildup 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 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. So how can we measure the DP? Placing taps both before and after the filter, a differential pressure measuring instrument can be connected to detect the high side and close 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 is derived from a calculation that factors in the flow rate, fluid viscosity, and filter characteristics.

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 line or static pressure level.

For more information on pressure measurement, call Mead O-Brien at (800) 892-2769 or visit www.meadobrien.com.

Here is a great video, courtesy of Ashcroft, that provides an excellent visual understanding of differential pressure.



Sunday, March 20, 2016

Types of Pressure Measurements Used in Process Control

Ashcroft pressure gauge
Pressure gauge
(courtesy of Ashcroft)
Pressure, the measure of a force on a specified area, is a straightforward concept, however, depending on the application, there are many different ways of interpreting the force measurement.

As with any type of measurement, results need to be expressed in a defined and clear way to allow everyone to interpret and apply those results correctly. Accurate measurements and good measurement practices are essential in industrial automation and process environments, as they have a direct effect on the success of the desired outcome.

When measuring pressure, there are multiple units of measurement that are commonly used. Most of these units of measurement can be used with the international system of units, such as kilo, Mega, etc.

This white paper (courtesy of Turck) will identify the various units of pressure measurement, while discussing when and why certain pressure measurements are used in specific applications.