5
Model 351/352/353 Liquid Level Systems
Section 1
The S048 sensor is constructed with the same housing as the 500-psi SWP sen
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sor for mounting purposes, but has no pressure rating and is designed to mount
inside open ves sels or sumps. The large bottom opening of the sensor prevents
fouling of the sensor ports due to dirt, loose debris, or other contamination.
Model 353 Liquid Level System
The Model 353 system is designed specifically for unusual fill liquid require
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ments due to liquid volumes or high ambient temperatures.
A Model 353 system can be designed with one or two sensors. Systems are
typically assembled in the field.
The Model 353 high-volume sealed sensor is rated for a 3,000-psi SWP and
contains a single removable bellows with an initial volume of 10 in.³ (164
cc). The bellows is 2.25 in. (57 mm) long and has a diameter of 3.75 in. (95
mm). It can extend an additional 1 in. (25 mm), adding an additional 7.5 in.³
(123 cc) to its volumetric capacity (see Figure 1.2). When the bellows is fully
compressed, an internal valve closes to prevent the escape of process fluids.
The bellows may be removed for replacing a dam aged bellows or for pressure
testing the capillary tubing.
Travel to
close valve
0.84 in. (21 mm)
Normal length
2.25 in. (57 mm)
1 in. (25 mm)
Expanded bellows
(hot condition)
Figure 1.2—Model 353 bellows travel (approximate dimensions)
Sensor Housings and Capillary Tubing
All sensors have stainless steel housings. Capillary tubing connecting the sen
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sor to the DPU is either 1/4-in. or 3/16-in. OD. Tubing length is deter mined
by the installation. Capillary tubing may be bent or looped as required. A
1/4-in. NPT plug or a high-pressure fitting (3/8-in. OD tubing) in the housing
facilitates venting.
