Mechanical Pressure Gauges Installation and Operating Instructions

Author: WIKA
From: WIKA Learning Center

Pressure Range Selection

To insure proper operation and long service life, the proper pressure range should be selected. For applications with constant, steady pressure, the measured pressure should be no more than 75% of the full scale range of the gauge. For applications with fluctuating pressure, the measured pressure should be no more than two-thirds of the full scale range of the gauge.

In general, it is best to choose a range that is roughly 2X the average measured pressure. This gives good over pressure protection and the highest accuracy.

Pressure Gauge Installation

The pressure gauge should be installed where exposure to heat and vibration are minimal and where the dial can be easily read. It is also important to install the gauge in a location with undisturbed and continuous flow of the pressure medium.

It is recommended that an isolating device, such as a needle valve or gauge cock, be installed between the process and the pressure gauges. This allows the gauge to be taken out of service without interruption of the process.

Connections with tapered threads, such as NPT, should be sealed by using PTFE tape (or an equivalent sealing compound) on the thread. Metric threads such as G1/4A or 1/4BSP should be sealed by using the appropriate sealing washer.

The gauge should be tightened and loosened using the wrench flats on the gauge socket. Never grasp the case to thread the gauge into the pressure system fitting. Doing so may cause irreparable damage to the gauge. For pressure gauges with flanged connections, care must be taken not to accidentally loosen the bolts that hold the upper and lower housings together.

A pressure gauge should never be removed when it is pressurized. Make sure the pressure system has been fully vented prior to removing a gauge.

Residues from the pressure medium may remain inside the pressure gauge after it has been removed from service. If these residues are hazardous or toxic, take the necessary precautions when handling and storing used gauges.

 

Isolating Devices

The isolating device may be either a pressure gauge cock or a needle valve, depending on operating conditions and requirements.

Pressure Gauge Cocks

Pressure gauge cocks have three handle positions:
OFF      The pressure medium is blocked and the pressure gauge system is open to the atmosphere.
ON        The pressure gauge is open to the pressure medium.
VENT   The pressure gauge is isolated but the pressure system is vented and the medium can escape into the atmosphere.Pressure gauge cocks should be installed so that when vented, the pressure medium is directed away from the operator.

Pressure Gauge Needle Valves

Needle valves also isolate the pressure gauge from the pressure medium, but they usually do not have any venting capabilities. Needle valves do have the advantage of restricting the flow of the pressure into the gauge which helps reduce damage by pressure spikes.

Pressure Gauge Mounting Options

If the pressure system or tee-extension cannot support the weight of the instrument, then surface or wall mounting brackets or mounting flanges (front flange or rear flange) should be used.
 

Vibration Protection for Pressure Gauges

If the pressure gauge is exposed to vibration or pulsating pressure or both, then a liquid filled pressure gauge is recommended. The liquid dampens the effects of vibration making the pointer easier to read.

 

Pressure Gauge Temperature Limits

The pressure gauge should not be used outside of its rated temperature limits as noted on the Data Sheet specific to that gauge. At temperatures above or below these limits, the gauge accuracy will be significantly reduced and the possibility of gauge failure may exist.
 

Overpressure Limits on a Pressure Gauge

WIKA gauges are generally designed to withstand up to a 130% overpressure without damage to the pressure system. For applications with overpressure spikes, a snubber or restrictor should be used. Snubbers and restrictors reduce the inlet size of the pressure gauge which causes the pressure to increase or decrease more slowly into the gauge. For applications with periods of constant overpressure, an overpressure protector should be used. The overpressure protector isolates the gauge when the pressure reaches a preset pressure value.

Tee Extensions Guidelines for Pressure Gauges

Tee extensions should have a diameter of at least 0.24 in. (6mm) to avoid clogging from solids in the pressure medium. WIKA recommends that long, horizontal tee extensions be sloped to about 1:15.

With a gaseous pressure medium, the extension should having a drain plug at its lowest point, while a line with a liquid medium should have an air bleeding valve at its highest point. A filter or separator should be used when the pressure medium contains suspended matter.

If a static head of liquid is acting on the gauge, then this causes a zero offset which affects the reading of the gauge.

The corresponding indication will be lower by the value of Δp if the gauge is mounted above, but higher by the value of Δp if the gauge is mounted below the pressure tapping point.
 

Pressure Gauges in Service

Always open isolating devices slowly. Opening them too fast may generate sudden pressure surges that could damage the gauge.

Calibration can be confirmed in larger diameter gauges (> 4") by checking the position of the zero point. To do so, close the isolating device and vent the gauge to zero pressure. The pointer must over the zero box . Unless the gauge temperature is significantly higher or lower than 68°F (20°C), a pointer not returning to zero may indicate that the gauge has been seriously damaged.

Pressure Gauge Storage

The pressure gauge should remain in its original packing until installation.

Storage temperature should not exceed -4°F (-20°C) or 140°F (60°C) unless specified otherwise. Consult the data sheet pertaining to the pressure gauge model.

Pressure gauges removed from service should be protected from dust and humidity, preferably by using the original packing material. Residue from the pressure medium may remain in the gauge and is susceptible to temperature influences (i.e. freezing). This should be considered when storing the removed pressure gauge.
 

Pressure Gauge Safety

Pressure media such as:

• Oxygen
• Acetylene
• Flammable gases or liquids
• Toxic gases or liquids
• Steam
• Ammonia and other refrigerants

as well as portable or stationary pressure systems like:

• Air compressors
• Welding equipment
• Pressure vessels and boilers
• Life support equipment

may require pressure gauges that have been tested and/or certified to national standards and/or local safety codes. Your local WIKA representative will be able to assist you in selecting the proper gauge model.

Standards for Pressure Gauges

U.S. & Canadian Standards are set forth by The American Society of Mechanical Engineers, which publishes pressure gauge specifications in their document ASME B40.1. This document specifies standard pressure gauge types, sizes, materials, ranges, and accuracies. Copies of this standard can be purchased directly from ASME:

 

ASME
22 Law Drive, Box 2900
Fairfield, NJ 07007-2900
1-800-THE-ASME or (973) 882-1167
Fax: (973) 882-1717
E-mail: infocentral@asme.org

 

European Standards are developed and published by the European Committee for Standardization (CEN) and replace the individual standards formerly used in each European country (such as DIN standards in Germany). Copies of these standards can be obtained through:

 

Comité Européen de Normalisation (CEN)
Central Secretariat
rue de Stassart 36
B-1050 Brussels
Belgium

 

Pressure Gauge Accessories

 

 

1. Over Pressure Protector
2. Throttling (adjustable) Snubber
3. Adaptor for wall mounting bracket
4. Needle Valves
5. Coil Siphon
6. Wall Mounting Bracket
7. Thread Adaptor (1/4" NPT - G1/4A)
8. Pressure Gauge Cock



 

Recommended Pressure Gauge Orientation

The table below shows the recommended position for pressure gauges in typical applications.

 

 

If you would like to receive more information about WIKA pressure gauges please contact Forberg Scientific, Inc. customer service.
Phone: 855-288-5330

Email: mechanicalsales@forberg.com
Websites: www.forberg.com & www.autoctrls.com
Download document: Installation and Operating Instructions for Mechanical Pressure Gauges



Recurring Gauges Failure can be Expensive and Risky

Author: Instrument Guru
Posted: WIKA Blog Dec 19,2013

There are plenty of articles and sites about automobiles and their woes. In an era of sophisticated cars packed with a myriad of electronic gizmos and digital instrumentation, quality gauges are essential to an automobile’s longevity—and its owner’s long-term happiness.

The same principle holds true in a processing operation: just like the devoted car owner, you depend on quality gauges for guidance, and you’ve learned that recurring gauge failure can signify a problem that must be remedied before it snowballs.

Moreover, while personal safety is at the top of everyone’s list in automotive transportation, quality gauges are especially important to the safety in a processing environment. Gauge failure in an plant can have far-reaching ramifications: a true crisis might affect hundreds, if not thousands, of people.

Just as that erroneously blinking light on your dashboard might ultimately cause you to ignore your gauges altogether, a recurring gauge failure might have the same effect in your facility. That’s not a good thing. We’ve all seen the statistics on how big disasters can often be traced to small gauge failures. OSHA statistics on just how much even one workplace accident can cost—in time off, in remedying the situation, and, possibly, in paying government fines – is substantial.

Therefore, money spent on quality gauges is usually well spent, and that it doesn’t pay, in the long run, to skimp on quality or service. Not only will your operation have reliable gauges available, you’ll benefit from knowing your equipment is backed up by a quality supplier with attentive customer service. The cost to your plant may be larger at the outset, but avoiding frequent replacement and  risks will pay dividends over time.

Those costs don’t even take into account the intangible benefits of owning quality instrumentation. You can’t always assign a cost value to “peace of mind,” but in an industry characterized by often-unforeseen hazards, it is indeed priceless.

So, too, is the goodwill, in the workplace and the community that comes from creating a safe, quality-conscious environment. People appreciate working in settings where their safety is paramount and they tend to hold onto such jobs. In a time when technical talent is becoming scarce, spending less time and resources on recruiting and training workers is a valuable benefit.

If you are dealing with a recurring gauge failure, where can you turn for help? Your first resource should be WIKA’s Full Audit Service Team (FAST). FAST is a value-added service that WIKA provides to its customers at no additional cost.

WIKA’s instrumentation engineers can quickly diagnose the reason for a recurring gauge failure. It might be as simple as a misapplied gauge or it could be a sign of a more complex problem requiring attention. The FAST team will identify the root cause and provide you with valuable solutions.

The FAST team provides a wide range of instrumentation services such as safety training, instrument audits, supply-chain streamlining, and more. Download a copy of “Navigating a Mine Field & Staying Safe,” WIKA’s e-book for the downstream petroleum industry. This e-book details how the FAST team can help you solve the riddle of recurring gauge failures and keep your plant safe and productive.

WIKA eLearning Click Here

If you would like to receive more information about WIKA pressure gauges please contact Forberg Scientific, Inc. customer service.
Phone: 855-288-5330
Email: mechanicalsales@forberg.com

Don't Neglect Pressure Gauges

Inadequate attention can make plants vulnerable to mishaps

From: WIKA Jason Deane

The simple pressure gauge is an often-overlooked defense mechanism for preventing accidents. However, in auditing more than 250 plants, WIKA Instrument discovered that up to 25% of all pressure gauges were broken, damaged or misapplied — this represents an average of eight deficient gauges located within 20 feet of each employee.

A failed gauge compromises a plant's ability to detect a problem before a safety incident occurs. Malfunctioning gauges also can lead to media leaks, fugitive emissions and a fire or explosion, taking a toll on safety and reliability.

Even minor accidents can cause employee injury and lead to downtime. Any accident or leakage also puts staff sent to fix the problem into harm's way, which, of course, can lead to further employee injury and lost hours.

Many causes contribute to this dangerous situation with gauges. Fortunately, they can be prevented.

CAUSES OF GAUGE FAILURE

Through its evaluation of more than 150,000 gauge installations, WIKA has identified eight common causes of failure. So, let's look at each, along with the solution.

1. Vibration. Many pieces of equipment vibrate. However, excessive vibration can lead to gauge failure and may indicate a problem with a component. Solution: install a gauge that will resist vibration better — i.e., a liquid-filled or direct-drive gauge with only a single moving part.

2. Pulsation. A rapidly cycling medium within a pressure system can make a gauge pointer move erratically and eventually can lead to breakdown of internal parts. Solution: install a restrictor and liquid-filled case to dampen pulses on a standard gauge or replace with a direct-drive gauge that lacks gears and linkages.

3. Temperature. Extreme temperatures cause sweating and loosening in metal joints and eventually can cause them to crack. Solution: install a gauge with a fully welded diaphragm seal and consider adding an on-board cooling element to combat the highest temperatures.

4. Overpressure and pressure spikes. Frequent pegging against the stop pin can bend the gauge pointer and compromise the integrity of the Bourdon tube or sensing element and, ultimately, lead to rupture. Solution: install an overpressure protector to inhibit readings that exceed gauge capacity.

5. Corrosion. The highly corrosive media often found in process plants can damage the sensing material in gauges. Solution: install a diaphragm seal that's constructed from material that will withstand the corrosive.

6. Clogging. A medium that contains suspended particles or is viscous or can crystallize can clog the pressure system and make gauge readings unreliable. Solution: install a diaphragm seal with a clog-preventing barrier.

7. Steam. Some media produce steam or other vapors that can damage the internal parts of gauges. Solution: install either a mini-siphon with an internal chamber to reduce surges or a full siphon, making sure to include a coil for horizontal applications and a pigtail for vertical ones.

8. Mishandling and abuse. Even properly installed gauges will start to malfunction if mistreated over time. Solution: conduct regular safety and maintenance training for all employees who come into contact with or proximity to gauges.

Unfortunately, many plant personnel aren't properly equipped or experienced enough to recognize and address all these problems. That, however, doesn't reduce the importance of doing so.

TACKLING THE PROBLEMS

When beginning to address instrument shortcomings, keep in mind that studies show that fewer than 0.25% of piping components account for greater than 80% of controllable fugitive emissions. Installing gauges with welded diaphragm seals on these components creates a dual containment device, which is required by the U.S. Environmental Protection Agency. This means plants can correct a major source of violations and fines by addressing a very small percentage of connection points. For many facilities, this is an excellent place to start to get meaningful results quickly.

Another fairly straightforward step that's simple to implement but can yield powerful results is standardization of gauges. This reduces the number of replacement parts that must be kept in inventory — and confusion by technicians. In other words, when replacing an old or faulty gauge, employees more likely will select the correct gauge rather than resorting to like and kind replacement. This also helps ensure the storeroom maintains proper inventory, helping cut costs.

Plants that don't have the resources to identify and correct faulty and misapplied pressure measurement instruments can get outside help, such as from WIKA's FAST Team. Any audit team should:

• Visually evaluate the plant's gauge population and look for issues that need to be addressed.
• Diagnose gauges that pose threats and uncover the causes.
• Formulate a strategic plan to address all the discovered issues.
• Audit the storeroom and streamline inventory, reducing redundant part numbers and guesswork.
• Provide dependable processes to prevent misapplying instruments in the future, and coordinate employee-training programs.

Given the complexity of managing the operations of a process plant, it's easy to understand how smaller components such as mechanical pressure instruments can be overlooked. However, using gauges as early warning devices can improve uptime, safety and profits. Money spent on the humble gauge very well could be the best investment a processing plant can make.

If you would like more information, pricing and availability on WIKA Pressure Gauges or other WIKA Instrument products please contact Forberg Scientific Customer Service.
Tool Free: 855-288-5330Email: mechanicalsales@forberg.com