The Ups and Downs of Pressure

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

The Ups and Downs of Pressure

Higher and lower pressures can occur in what seem like unusual circumstances.  In plumbing, for example, much higher pressures occur if air gets into a water line and the faucet is closed quickly. Called water hammer, the effect causes audible noise or the banging of pipes. The hydraulic shock wave can, in some cases, cause severe damage since the pressure is so high. Draining the system is the usual solution to this problem.

On the down side, many people are surprised when they open a refrigerator door, close it and then try to immediately reopen it. The negative pressure in the refrigerator caused by this activity can be so extensive in well-sealed systems that it takes significant forced to re-open the door. The decreased pressure results from cooling of the warmer air entering the refrigerator. Based on ideal gas law, the pressure decrease could be 10% or more. In deep freezer units and those with the best sealing, the effect is even stronger producing even lower pressures.

Ideal gas law: P V = n R T

Where: P is the pressure, V is the volume occupied by n moles of any gas at temperature (T) in Kelvin and R is the gas constant.

Central Restaurant Products Walk-In Freezer

Walk In Freezer courtesy of Central Restaurant Products.

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Pressure to Heal

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Pressure to Heal

Applying pressure to a wound is the first step toward the healing process. This could be something as simple and commonplace as getting a vaccination or having blood taken where the pressure is simply applied by a finger. For a more life-threatening wound, a tourniquet might be required. But how much pressure should be applied?

Sufficient pressure needs to be applied to stop the flow of blood so clotting (occlusion) can occur. If blood flow cannot be stopped at the site, direct pressure to an artery may be required. For medical professionals, the term limb occlusion pressure (LOP) is used. This is “the minimum pressure required, at a specific time by a specific tourniquet cuff applied to a specific patient’s limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff.”

For hospitals an Automatic Tourniquet System provides a means of monitoring and controlling the applied pressure. In an operation, equipment such as the Zimmer A.T.S. 3000 uses LOP technology to sense, calculate and report the cuff pressure necessary for complete blood occlusion in the operative limb. Applied to the index finger or second toe of the patient’s operative limb prior to the surgical procedure, the LOP sensor in the A.T.S. 3000 provides a recommended tourniquet pressure (RTP) setting in approximately 30 seconds.

Zimmer’s A.T.S. 3000 Tourniquet System

Personalized Pressure™ Technology in Zimmer’s Tourniquet System, such this A.T.S. 3000, delivers the minimum amount of tourniquet pressure at a specific time, with a specific cuff, for a specific limb. Image courtesy of Zimmer Biomet.

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Working Pressure

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Working Pressure

Numerous applications rely on pressure to work properly. The specific working or operating pressure may vary greatly between applications and it often must be maintained within a reasonably narrow window for optimum performance or to stay within a safe range or below a maximum value for safety. Working properly versus improperly and even under abnormal conditions has implications as well for pressure.

For pressure vessels, especially those in industrial applications, the terms maximum allowable working pressure (MAWP), and design pressure are used. The design pressure is determined from its maximum operating pressure (MOP) which is typically increased by some margin to handle potential pressure surges. In contrast, MAWP is the maximum pressure at which the vessel or equipment is allowed to function at a specific temperature and, in some cases, is determined by design codes.

Maximum Allowable Operating Pressure (MAOP) is another pressure limit, usually established by a government body, that is less than the MAWP. To be safe, the pressure could be monitored in the application to alert an operator or execute an automatic shutdown if an unsafe condition is reached.Operating Pressure Diagram

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Pressure – A Class Act

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Pressure – A Class Act

That’s right. For the piping industry, the American National Standards Institute (ANSI) developed Pressure Classes (or ratings) for different types of flanges used in industrial applications.

According to ASME B16.5, forged steel flanges are made in seven primary Pressure Classes: Class 150, 300, 400, 600, 900, 1500 and 2500. More recently called “ANSI class,” the designation for the pressure-temperature rating of a pipe flange  is a dimensionless number. Because it is constructed with more metal, a Class 300 flange can handle more pressure than a Class 150 flange. However, a Class 150 flange is rated to approximately 270 PSIG at ambient conditions, 180 PSIG at approximately 400°F, 150 PSIG at approximately 600°F, and 75 PSIG at approximately 800°F.

American National Standards Institute

Image courtesy of the American National Standards Institute.

Determining or verifying the pressure rating or monitoring the pressure in an application could be accomplished with an appropriately rated All Sensors SPA 402 Series of stainless steel, media-isolated pressure sensors.

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