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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.
Wastewater
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:
- There must be a DUAL barrier between the media and the
conduit; and
- The secondary barrier must be rated to the process; and
- 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.
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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 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.
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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, 119
Series, and Spectra 12 For Class I, Div. 2 only: The H117 Series For
NEMA 4X: The H100 Series
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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.
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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
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
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 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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