Masoneilan 12820 Pneumatic Level Transmitter
Overview
The Masoneilan 12820 is the pneumatic level transmitter of the Baker Hughes 12800 Series. It controls nothing itself: it measures the level of a liquid, or the position of the interface between two liquids, with a displacer and torque tube and sends the result as a pneumatic signal, normally 3-15 psi, to a receiver such as a panel indicator, recorder or separate pneumatic controller. Because the signal is air, the Masoneilan 12820 needs no electrical wiring.
Seven Star LLC supplies the Masoneilan 12820 to oil, gas and process plants across Oman and the GCC, including customers who need a like-for-like pneumatic replacement in an existing loop. We confirm displacer range, chamber arrangement, specific gravity and output range from the nameplate and provide the Baker Hughes manual for alignment after connection to the receiver.
Operating Principle of the Masoneilan 12820
As the level rises the displacer is buoyed up and its apparent weight falls, so the torque tube turns a small amount. The reversing arc carries that motion through a control link to a control arm that moves a flapper relative to a nozzle. A relay amplifies the nozzle pressure and a feedback bellows returns part of the output to the arm, so output pressure is proportional to level change across the chosen span.
Baker Hughes describes the transmitter mechanism as similar to that of the proportional controller with two changes: the control setting cam is replaced by an alignment micrometer and lock, which fix the zero, and the proportional band adjustment becomes a proportional micrometer with a micrometer spring, which fixes the span. A transmitter scale replaces the proportional band scale, and no set point or control action is needed because the output is simply a measurement.
Engineering Design of the Masoneilan 12820
A chamber model of the Masoneilan 12820 mounts vertically at the side of the vessel with the mid-range mark at normal level, equalising lines the size of the chamber connections and a block valve in each line. An internal displacer hangs in the vessel and needs a guide bracket in moving liquid or a stilling well in turbulent liquid. Output air is piped in 1/4 in. brass pipe or 3/8 in. O.D. copper tubing that must be air-tight. The case can be reversed in the field by moving the torque tube housing to the opposite side of the protective housing and turning the reversing arc over.
Mounting Details and Specific Gravity Range of the Masoneilan 12820
On a top-flange model the displacer can be attached before the chamber flange is bolted to the nozzle flange, and where overhead room is short a detachable hanger extension is screwed into the displacer and pinned before the unit is lowered. A side-flange model needs a manway, because the displacer is attached after the flange is bolted, by reaching into the protective housing and depressing the torque arm. A guide bracket hole should be 1 to 1.5 in. larger than the displacer for ranges to 6 ft and 2 to 3 in. larger for longer ranges, with the bracket 2 to 3 in. above the displacer’s lower end.
The reversing arc scale is graduated for specific gravities down to 0.5, but the standard displacer of the Masoneilan 12820 can serve gravities, or interface gravity differences, as low as 0.1. The control link index is then set at 0.5 and the transmitter scale values become relative, so the actual band is read from the curves in the manual.
Alignment of the Masoneilan 12820
The manual states that the transmitter must be adjusted after it is connected to the receiver. With the displacer hanging free, set the control link index to the specific gravity, turn the proportional micrometer to 100 and lock it, then adjust the alignment micrometer for 3 psi. Raise the level to the top of the range: if the output is below 15 psi, narrow the transmitter band with the proportional micrometer; if above, move the clamp the other way. Re-trim the alignment micrometer for 15 psi, then lower the level to zero and confirm 3 psi, repeating until both ends read correctly and locking the clamp screw and micrometer lock after each adjustment.
Key Features
- Transmits level or interface level as a pneumatic signal without electrical power.
- Zero is set with the alignment micrometer and span with the proportional micrometer, each with a lock.
- A transmitter scale gives a direct reference when span is adjusted.
- The Masoneilan 12820 compensates for specific gravity on the reversing arc and supports interface service.
- Output of 3-15 psi or 6-30 psi with supply set to 20 psi or 35 psi.
Industrial Applications
A pneumatic transmitter is the right choice when a level signal must reach a receiver using only instrument air. The Masoneilan 12820 can feed a level indicator, a recorder or the set input of a separate controller in refineries, gas plants and chemical units, and it can pair with the pneumatic set controller of the same series where cascade or remote setting is needed. In Oman it serves established plants at Sohar, Duqm and Salalah where pneumatic loops remain in use.
On the receiving valve it works with the Masoneilan SVI FF valve positioner and actuators such as the Masoneilan Type 87/88 spring-diaphragm actuators.
Related published Masoneilan pages: Masoneilan 10000 Series double-port valve.
Technical Specifications
Published data for the Masoneilan 12820 from the 12800 Series instruction manual.
| Parameter | Specification |
|---|---|
| Model | Masoneilan 12820 pneumatic level transmitter |
| Function | Level or interface level transmitter with pneumatic output |
| Output signal | 3-15 psi or 6-30 psi |
| Supply | 50 to 125 psi gauge to the filter regulator, then 20 psi or 35 psi |
| Zero adjustment | Alignment micrometer with lock |
| Span adjustment | Proportional micrometer with clamp screw, set to 100 at the start |
| Alignment check | 3 psi at zero level, 15 psi at top of range |
| Mounting | Chamber on the side of the vessel, or internal displacer on a top or side flange |
| Case and connections | Not above 180 degF at the case; 1/4 in. NPT supply and output |
| Service life | 25 years or more with annual inspection |
Related Masoneilan level instruments include the Masoneilan 12800 Series pneumatic level controller, Masoneilan 12400 Series digital level transmitter, Masoneilan 12810 proportional-reset level controller, Masoneilan 12830 differential-gap level controller and Masoneilan 12840 pneumatic-set level controller.
Request a Quote for Masoneilan 12820
Request pricing for the Masoneilan 12820 by sending an RFQ to the Seven Star LLC instrumentation division with the displacer range, mounting type, specific gravity or interface data and the signal range of the receiver. We confirm the model, advise on availability and lead time and provide the Baker Hughes instruction manual from this page. Seven Star LLC is the trusted supplier for Masoneilan in Oman and the GCC.
- Instruction Manual Masoneilan 12820 Level Transmitter Instruction Manual Download
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