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Реле производства United Electric можно найти во многих отраслях промышленности и приложениях, начиная с нефтеперерабатывающих заводов и заканчивая лабораторным оборудованием. Ниже приведены примеры отраслей промышленности и приложений для продукции  компании United Electric. Если Вы хотите поделиться своим опытом, пожалуйста, напишите нам: sales@ueonline.ru.


Problem: For many applications in waste-water facilities, there is a need for alarming, monitoring and local indication of pressures. When sensing sludge and slurries, an isolator ring is used to prevent plugging of the pressure instrumentation ports. For cost and space reasons, multiple instruments are frequently mounted in a piping "T" arrangement to the isolator. There are some problems with this type of assembly. Where a pressure switch and gauge are combined, there may be as many as 9-10 potential leak points in the piping assembly! A leak at any point would render the entire assembly non-functional, exposing the pump or process to damage. In addition, the space needed for such an assembly is large, typically 1.5 to 2 sq. ft. And, finally, the cost for installing, calibrating and maintaining these assemblies can also be high.

Solution: United Electric Controls' One Series Switch is a cost-effective alternative to the typical mechanical gauge and switch assembly. By mounting the One Series directly to the isolator ring, the potential leak paths are reduced from 10 to 2. Switching and indication are simplified, done by the same instrument. The addition of an optional 4-20 mA analog process monitoring signal can also be provided, thereby combining a total of three functions in a single instrument! Another benefit is the greatly reduced size. The result is that overall reliability is significantly increased and calibration/testing becomes much easier.


Compliance with NEC 501-5 (f)(3) for Class 1 areas

Problem: Section 501-5 of the National Electric Code deals with the sealing and draining of conduit systems in Class 1 areas. Paragraph (f)(3) is specifically concerned with preventing flammable or combustible process fluids from entering the conduit system. The full text of the paragraph is noted below, but, briefly, it states that:

  1. There must be a DUAL barrier between the media and the conduit; and
  2. The secondary barrier must be rated to the process; and
  3. There must be a visible indication that the primary barrier has failed.
Many plants use a combination of a pressure switch and filled diaphragm seal to isolate the conduit from the process. This does not meet the intent of the Code since there is no visible means of detecting the primary leak. It is insufficient to use a conduit seal-off for this purpose.

Solution: United Electric Control's 119 Series of pressure switches incorporate design features to meet the NEC standard. With single or dual output, both series have a variety of materials and pressure connections to meet most application requirements. They utilize a combination of the enclosure and a hermetically-sealed microswitch to provide a secondary barrier. Visible indication of a leak is available by specifying an option for a tapped hole through the side of the enclosure. The H119 and H119A have a 316 stainless steel enclosure for added ruggedness.


API 610 Applications

Function: Reservoir systems and buffer gas systems are accessory items for pumps and compressors. Reservoir systems provide cooling and lubrication to pump or compressor seals. Buffer gas systems work in conjunction with reservoir systems in applications that require pressurization of seals to a pressure that is higher than the process pressure. The seal is pressurized through an air-over-hydraulic arrangement in which high pressure buffer gas is applied to the buffer fluid. The buffer gas system helps to unload the seal and reduce friction thus enhancing the life of the seal.

Problem: Reservoir system and buffer gas system requirements are regulated by API 610. Following this standard can help increase the equipmentнs life by assuring proper lubrication and protection. Since most rotating equipment found in process plants has a high economical value, poor protection of the pump and compressor seals could result in costly consequences. Also, any leakage of hazardous media from these systems may endanger the environment or personnel associated with the equipment.

Solution: As the reservoir system protects the seals, it is critical to monitor the pressure within the reservoir. As the pressure builds to a critical threshold point, a pressure switch can act as a watchdog and sound an alarm that the normal operating parameters have been exceeded.


Firesafe Applications

Problem: The installation of instrumentation in refineries, chemical plants and other hazardous locations pose some unique problems. Since many of the materials which are sensed and processed in these plants are flammable, fire-safety is one area of particular concern. Processes must be designed so that, in the event of a fire, the fire can be contained and controlled. Unfortunately, many instruments are not designed for this service. High heat can cause these instrument housings to melt, freeing the contained media and feeding the fire further. To be "fire safe", instrumentation must be designed so that the pressure connection retains the sensed material. In general, the design will use an all-welded, 316 stainless steel pressure sensor. This construction must cause the pressure connection to remain plugged, even if the pressure-sensing diaphragm or the instrument housing is destroyed.

Solution: Many of United Electric Controls' products are standardly considered fire safe. The following product lines all have firesafe models: For Class I, Div. 1&2: The 120 Series, 119 Series, and Spectra 12 For Class I, Div. 2 only: The H117 Series For NEMA 4X: The H100 Series


Pressure switches: a cost-effective alternative to safety relief valves

Function: Safety relief valves are often used to limit pressure between stages of multi-stage rotary compressors. As pressure builds between stages, the valves open to relieve pressure and return the system to normal operating ranges.

Problem: Relief valves tend to leak or bleed off pressure during normal operations. For some media, including natural or synthetic oils mixed with air, this continuous venting causes problems. Specifically, in hazardous environments, leakage of the media could result in dangerous and costly consequences, particularly if this leakage is in violation of environmental regulation.

Solution: Replacing relief valves with pressure switches eliminates leakage problems. A pressure switch will detect the critical threshold point and shut down the process. The addition of a manual reset option will require the operator to restart the process when pressure returns to its normal operating range.


Prevent leakage from mechanical seals with reservoir systems

Function: As "add-on" packages for centrifugal and rotary pumps, reservoir systems prevent leakage to the atmosphere as described in API 610 and API 682. Installations, governed by either API Plan 52 or Plan 53, utilize dual mechanical seals with a buffer fluid between them. The system operates at atmospheric pressure in Plan 52 and slightly above process pressure in Plan 53. Depending on which Plan is selected, seal leakage is either retained in the reservoir or directed back to the process.

Problem: A reservoir system can help protect equipment and ensure compliance with safety and environmental regulations. But what protects the reservoir system? Whether the installation follows Plan 52 or 53, a high pressure condition could be catastrophic. Extreme pressures could indicate seal failure or a "runaway" process, which may lead to expensive pump repair or an environmental disaster. Similarly, loss of pressure in a pressurized system could result in premature seal failure or contamination of the buffer fluid.

Solution: As the reservoir system protects equipment and the environment, it is critical to monitor the pressure within the reservoir. As the pressure builds to a critical threshold point, a pressure switch can act as a watchdog and sound an alarm that the normal operating parameters have been exceeded. Pressure switches are also used on Plan 53 systems to indicate loss of buffer gas pressure.

United Electric switches provide all the features mandated by API 610 and 682, such as:

  • Over range pressure consistent with maximum system pressures
  • No affect by exposure to full vacuum
  • AISI 316 stainless steel wetted materials
  • Bellows or diaphragm sensing element
  • 1/2 NPT pressure connection
  • Hermetically sealed DPDT switch contacts

Marine Industry

100 series used in the marine industry: H100's and E100's were chosen by a company that builds annunciator panels for tug boats and supply vessels on the U.S. Gulf Coast. The H100 model 702 is used as a low-limit switch for water and lube oil pressure in the engine rooms of these boats.

The E100 model 2BS safeguards the engine by monitoring oil and water temperatures. Oil temperatures are alarmed at 220F and water temperatures at around 198 F. The switches are wired normally open and actuate on rising temperature.


Trash compacting

Typically the H100 and the 10 series is used to limit the action of the compactor's hydraulic mechanism to spare the electric motor from overloading when the compactor is full. The H100 or 10 series senses rising pressure. Another use involves wiring to a light panel to signal when the compactor is full.


Steam sterilization

UE F100 temperature switches are being used to measure the temperature of "seed transfer lines" used in the production of penicillin products. These transfer lines require periodic steam sterilization. The steam used in this cleaning process is pumped into the lines, raising the temperature to 120 C or more. The switches are placed at several points along the line and set at 123C. When the temperature is reached, the snap switch actuates a pilot light signaling the operator that the sterilization temperature has been reached.


Multi-stage liquid level control

A sensitive range is selected such as 0- 80"wc or 0- 20 psi. The height of the liquid determines the pressure exerted on the sensing element. In a sump application, the three pressure settings of the J403 correspond to "pumping out" elevations. Typically two (2) switches are wired to actuate pumps on rising level, cutting out on fall. The third switch serves as a high alarm, actuating a warning signal if pressure exceeds a given value.


Activating a overflow pump

Units are mounted on outside of a an overflow tank. J120-190 explosion proof units with an all welded stainless steel diaphragm are used to sense increasing head pressure when the tank fills.


Differential pressure switch warns of clogging filters

The H121K model 147 is used on the refrigeration compressors. The compressors supply coolant to large storage tanks where gas products are kept. The switch is mounted across an oil filter and is set to actuate an alarm if the differential pressure exceeds 4-5 psid. The cause of this excessive differential pressure would indicate a clogging or a clogged filter condition, something that could damage the compressor (and effectively halt the process) if not remedied. When used with the indicating scale option maintenance technicians receive an immediate, visual warning of clogging or clogged filter condition. This allows technicians to schedule maintenance on the compressor.


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