Pressure Controls manufactured by United Electric Controls
Pressure Control Applications | United Electric


United Electric pressure controls can be found in many industries and applications, from refineries and process plants to lab equipment. Below are just a sampling of industries and applications for UE products. If you'd like to share your applications, please e-mail us at

Application Notes (PDF)

Seal Oil Skid Cost Reduction

One Series Success Story


Intrinsic Safety

An alternative to explosion proof NEMA 7 & 9 enclosures, intrinsically safe electronic instrumentation may be used in Class I, Division 1 Ex ia (ZONE 0) areas when suitable safety barriers, entity parameters and proper wiring procedures are provided. The One Series 2-Wire electronic pressure switch and temperature switch model 2W2D is approved for use in intrinsically safe (Class I, Div. 1 Ex ia, ZONE 0) applications.

In the past, UE recommended the MTL5012S barrier exclusively. While this barrier continues to be available from MTL, UE now recommends any safety barrier that adheres to the NAMUR standard for proximity switches may be used to achieve intrinsic safety with the One Series model 2W2D. This includes other barriers from MTL and Pepperl+Fuchs (P+F) that adhere to the NAMUR standard for proximity switches. Recommended barriers by P+F include:


The One Series is also compatible with standard 28-volt diode barriers supplied by most major manufacturers including MTL 7087+ and Pepperl+Fuchs Z787.

PLEASE NOTE: The One Series 2W2D is the only model that is approved for use in intrinsically safe areas. Without the safety barrier, all One Series models are approved for Division 2 Hazardous locations. For additional information, please refer to the following accessory drawings:

A-62174-19 (for N. America)
A-62174-20 (for Europe).

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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.

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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 12 Series pressure switch incorporates design features to meet the NEC standard. The 12 Series utilizes a combination of the 316 stainless steel enclosure and a hermetically-sealed micro switch to provide a dual barrier. Visible indication of a leak is through a weep hole located underneath the attached nameplate. Since the 12 Series has models designed with a variety of sensor materials and pressure connections, it is able to meet most applications.

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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 equipment's 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.

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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 and Spectra 12 For Class I, Div. 2 only: The H117 Series For NEMA 4X: The H100 Series

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Pressure Controls: 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.

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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
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Marine Industry Control

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.

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Trash Compacting Pressure Control

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.

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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.

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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.

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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.

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Differential pressure control 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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