900 Series ABS & Stainless Steel Liquid Filled Pressure Gauges

A: A fill plug seals the fill hole in a pressure gauge case. On liquid filled pressure gauges, a ventable fill plug is used to relieve internal case pressures that occur due to thermal expansion of the fill fluid. In non-filled dry gauges, a non-ventable fill plug is used to occasionally drain the interior of the case from condensate or relieve internal case pressures. Ventable fill plugs incorporate a vent pin to open and close a hole for relieving internal case pressures and do not have to be removed from the case hole like non-ventable fill plugs.

A: Overpressure ratings are specific to the gauge type, pressure range and accuracy ratings of the gauge. Normal overpressure protection can range from 1.1 times to 1.3 times the full scale pressure depending on the gauge selected. NOSHOK gauges comply to the EN-837-1 and ASME B40.100 standards in regards to overpressure protection. When selecting a pressure gauge, it is recommended that the normal system pressure be maintained around half of the full range of the gauge as to avoid overpressure conditions.

A: A Maximum Indicating Pointer (MIP), also commonly referred to as a Tell Tale Pointer, adds an additional error to the pressure gauge due to the increase load on the bourdon tube. The lower the pressure range, the higher the error. Typically 1%. Consult factory.

A: Certified Calibrations provide the user with a serial numbered gauge along with a calibration certificate that it has been certified in accordance to the pressure gauge standard with instruments that are traceable to NIST with accuracies of at least 4 to 1.

A: A Certificate of Conformance is a formal statement on company letterhead stating that an instrument complies with a particular standard and/or specification. It contains the signatures of the required personnel. These Certificates are often needed to show industry inspectors that a system and its components are in compliance.

A: NOSHOK pressure gauges require little or no calibration within the Warranty period. Some applications may be more aggressive than others, resulting in an increased frequency in the need for calibration. The environmental limitations for the pressure gauge series should be observed in all cases. Gauges used in situations outside these requirements may result in inaccuracies, premature wear and/or failure of the gauge and would require additional maintenance. The frequency of calibration, therefore, is best left to the user to determine.

A: Orifices are a type of snubber. On pressure systems that have rapidly increasing or decreasing pressure spikes, orifices lessen the effects of these energy pulses by blocking the wave energy using restricted flow. They are recommended in dynamic pressure applications with mild pressure spikes.

A: A diaphragm is used to isolate and protect the instrument from the process media. Damaging process media may include corrosives, particulates, temperatures, or any state that is not suitable for direct contact with the measuring element. Diaphragms indirectly transmit system pressures by segregating the process pressure with a thin flexible membrane that in turn transfers the pressure through a fill fluid to the instrument. Diaphragms are often used in conjunction with capillaries to further distance the instrument from the process media. Capillary tubes transmit the diaphragm fill fluid to the instrument. Capillary tubes come in several lengths and provide the user a means to measure in a remote location and may also act as heat dissipaters in high temperature applications.

A: Primarily, in applications that have vibrations or pulsations, liquid filling enables reading the dial pointer by dampening the movement. Liquid filling should be considered in any system that has high dynamic operating conditions. In general, liquid filling helps extend the life of a gauge. It reduces damaging resonance induced fracturing, reduces frictional wear, prevents aggressive ambient air from entering, prevents condensation formation, and improves reliability.

A: Temperature changes affect the stiffness of a bourdon tube. The stiffness change is produced by a combination of changes in the elastic (Young's) modulus and a change in linear dimensions due to linear expansion and contraction. The error caused by temperature change will follow the approximate formula: ± 0.04 x (t2 ñ t) % of of the span.

A: The pressure range of a gauge should be a minimum of 10 percent over the maximum working pressure in static conditions with no pressure fluctuations. In dynamic conditions, the gauge range should be a minimum of 40 percent over the maximum working pressure. Ideally, the pressure gauge range should be selected for a midscale reading during normal operating pressures.

A: Accuracy is the difference between the true value and the gauge indication expressed as a percent of the gauge span. It is determined by comparing a gauge indication to a known standard or certified true value and combines the effects of method, observer, apparatus, and environment. Accuracy error also includes hysteresis and repeatability errors. An ASME B40.1 class B gauge has three accuracies. For example, a 3-2-3 percent of span designation stands for 3 percent in the first quarter of the scale, 2 percent in the middle half of the scale and 3 percent in the upper quarter of the scale.

A: Lens materials include Instrument Glass, Laminated Safety Glass, Tempered Glass, and plastic. Glass lenses are used for abrasion, chemical and wear resistant properties. Laminated safety glass reduces the possibility of shattering if the bourdon tube ruptures. Tempered glass is 2 to 5 times stronger than plain glass. Plastic lenses are used for impact, corrosion and chemical resistance. Special attention should be paid to the temperature and corrosive environments. Polycarbonate is selected for its superior impact resistance, acrylic for its clarity and scratch resistance and Homalite for its superior chemical resistance. In general, gauges with plastic lenses should remain below 140 degrees Fahrenheit.

A: Pigtail syphons should be used in steam applications and systems that contain superheated vapor. The pigtail buffers the instrument from the damaging effects of high temperature steam by holding system fluid in the coil to provide a steam trap for the fluid to condensate and dissipate the heat.

A: Cleaning for Oxygen (O2) service is performed on gauges that are used on oxygen service or oxidizing media applications. The cleaning removes all hydrocarbons, such as oil and grease, that can react violently, resulting in explosions, fire, and injury to personnel and property. Gauges cleaned for Oxygen service can be used in any application that requires the cleanliness level associated with oxygen cleaned gauges. Glycerin filled gauges cannot be used on oxygen systems or on other oxidizing media.

A: Glycerin is the most common fill fluid. Because of its unique fluid properties, Glycerin has become the standard for liquid filled gauges. Glycerin's clarity, viscosity, stability, cost, solubility and low toxicity make it an ideal fluid for many applications. Mineral oils and silicone fluids are used when temperature extremes, chemical compatibility or viscosity fall outside of Glycerin use. Halocarbon is an inert fluid that is compatible with chlorine, oxygen service and some high temperature applications. Glycerin is not compatible with strong oxidizers such as oxygen, chlorine, hydrogen peroxide or nitric acid. Glycerin and silicone are explosive in contact with chlorine. Halocarbon is explosive in contact with aluminum and magnesium.

A: The ASME B40.100 (formerly ASME B40.1) and EN 837-1 are both standards for pressure gauges, but they serve different regions and regulatory frameworks. ASME B40.100 is the U.S. standard for dial-type, elastic-element pressure gauges, providing guidelines for design, accuracy, performance, and testing. Primarily used in North America, it includes similar technical requirements to EN 837-1 within a mandatory appendix. EN 837-1, on the other hand, is the European standard specifically for Bourdon tube pressure gauges, enforcing strict requirements for dimensions, metrology, and testing to ensure compliance within the European Union. While both standards cover similar aspects of pressure gauge design and performance, EN 837-1 is a regulatory requirement for products sold in Europe, often necessary for CE marking, whereas ASME B40.100 serves as an industry guideline aligned with ANSI-approved U.S. standards.

A: Throttle devices limit the flow to the pressure instrument. They are a type of snubber.

A: The tip motion of a bourdon tube is translated to rotary motion of a pointer by a linkage and sector gear acting on the pointer pinion gear. Stop pins limit the movement of the bourdon tube, sector or pointer rotation in over and under pressure conditions that would otherwise move the pointer pinion off the sector gear and damage the gauge.