How to Solve Flanged Diaphragm Pressure Transmitter Oil Shortage failure Problem 

Diaphragm pressure transmitters are one of the most common instruments used in alumina production. Although diaphragm pressure transmitters are generally not subject to physical failure, the most common failures are zero-point drift, pressure sensor damage, and lack of oil.

Zero drift fault is generally can be manually adjusted with the hand operator, it can only be replaced if the pressure sensor is damaged, and many brands of pressure transmitter sensor is the overall package, simply can not be replaced or spare parts can not be procured, can only be scrapped; so only the lack of oil failure, the maintenance value is greater, most of the use of units as long as the diaphragm rupture or no oil, the usual practice is to scrap, resulting in great waste. Therefore, through the pressure transmitter oil shortage fault analysis and maintenance treatment, we can significantly improve the instrument’s utilization rate and service life and be in line with the requirements of energy-saving enterprises to reduce consumption.

1. Preface

Instrument fault repair is a significant part of the pre-use management of the instrument, and valuable repairs are the primary means of saving money on spare parts as we use the device. Although there are thousands of meters and hundreds of types in alumina production, it is impossible to have every meter in the warehouse. Therefore, only essential meters and common maintenance parts can be stocked.

Maintenance is essential when we have unplanned breakdowns and no spare parts to replace them, and storing too many spare parts is bound to increase equipment management costs. For example, there is a wide range of brands of pressurized transformers, and most of them have a purchase price of over RMB 5,000 to 10,000. If they are scrapped due to lack of oil alone, it will cause a significant waste. Therefore, it is more in line with the requirements of equipment management and the theme of energy-saving and consumption reduction of enterprises to improve the maintenance skills, enthusiasm, and creativity of technicians and reduce the dependence on spare parts.

2. Analysis of equipment condition and causes of an oil shortage.

2.1 Main parameters of the equipment

For example, a diaphragm pressure transmitter, model: 3051L3AA0TD11AAM5; range: 0 to 1.6 MPa; flat flange: DN80; accuracy: 0.5; supports HART protocol.

2.2 Analysis of the causes of oil shortage

Diaphragm pressure transmitter lacks oil performance in the diaphragm box no oil, diaphragm no flexibility, hand pressure diaphragm display no change. There are two main types of diaphragm failure: one is the instantaneous pressure is too large impact diaphragm rupture, the other is not tightened oil hole screws lead to silicone oil leakage; may also be used for too long equipment aging silicone oil seepage, so this situation can only be replaced the diaphragm and can be reassembled with the sensor damage and diaphragm intact pressure change.

In the absence of a range of professional equipment, the second case will require refueling. In addition, the membrane box must be prepared to work and repeatedly tested. Otherwise, it will directly affect the measurement accuracy of the equipment.

3. The repair process

3.1 Tools and materials preparation

Tools and materials required: digital pressure calibrator (with positive and negative pressure) for 0~1.6MPa; 1 piece each of connecting flange piece and gasket (DN80); 1 17~19 fork spanner; 2 32~34 fork spanners (or live spanners) 1 syringe; benzyl silicone oil (choose -10~180℃, depending on the actual situation); 1 hand-operated device; hexagonal 1 spanner (size 4).

3.2  Repair steps

The complete diaphragm pressure transmitter is shown in Figure 1. Whether or not the pressure change is short of oil can generally be felt without connecting a pressure calibrator by pressing the diaphragm by hand.

4. Diaphragm Pressure Transmitter

Prepare the tools and materials for the filling of the silicone oil in the following steps.

4.1 Remove the four hexagonal screws and one hexagonal screw from the connection part of the diaphragm box to the sensor.

4.2 After dismantling the structure, the diaphragm flange is connected to the prepared DN80 flange piece and gasket, fastened with bolts, and then connected to the digital pressure calibrator.

4.3 After completing the above steps, use a syringe to draw in an appropriate amount of silicone oil and set the digital pressure calibrator to negative pressure gear. Two people are required to slowly pressurize and simultaneously fill the silicone oil with a syringe from the filling hole.

4.4 We put the flange up slowly so that the position of the refueling hole is higher than the highest position on the edge of the membrane box, slowly pressurize the refueling, pressurize to around -70kPa, stop pressurizing and at the same time almost fill the membrane box with silicone oil.

4.5 When we slowly release the negative pressure, see if any air bubbles are excluded while continuing to pressurize and fill with silicone oil, and so on, discharging the excess air bubbles until no air bubbles are released.

4.6 When we release the negative pressure of the membrane box, we should fill it with silicone oil, fill the outside of the sensor diaphragm with silicone oil and then quickly tighten the bolts back together. In addition, it is more effective to make a funnel type refueling tool, simply place the funnel on top of the refueling hole, use the seal ring, etc. to make a good seal, pour the silicone oil directly into the funnel, use the negative pressure to self-priming, then release the negative pressure to remove the air bubbles, and so on, so that there is no need to worry about silicone oil overflow, more reliable.

5. Validation

When we have finished pressing the installation, we also have to carry out calibration; the calibration steps are as follows, use a standard meter to provide AC24V power supply to the diaphragm pressure transmitter and see if the pressure transmitter is zeroed without hitting the pressure if it is not zeroed it also needs to be connected in series with a hand operator to set the zero point.

5.1 After the successful setting of the zero point for the pressure test, we have to divide it into five average points to be checked according to the range of the pressure change.

5.2 Table 1 shows the original records of the pressure transmitter calibration records. The fundamental error and the return difference are calculated based on the tested point and the theoretical output value.

5.3 We allow an error of ±0.08mA and an allowable return of 0.08mA, according to the calculation formula.

It has a maximum error of -0.079mA and a maximum return of 0.078mA. From the data, its maximum error and maximum return are within the permissible measurement range. Then from the appearance, sealing, etc., if there is no problem, the meter is qualified. In addition to this, we have to consider the temperature and humidity at calibration, etc. If the calibration is not qualified, further commissioning is required, after which the calibration is carried out again, and so on until it is limited. If it cannot be allowed, it can only be scrapped.

6. Conclusion

The Diaphragm pressure transmitter refueling method seems simple, but if you ignore it quickly cause the silicon oil is mixed with air bubbles, affecting the pressure transmitter measurement effect. So many technicians see this situation. The first thing that comes to mind is to replace rather than repair, even if you think of repair and consider that there are no special oiling tools, no reference material, do not know where to start. Many times, the maintenance of equipment requires technicians to think more, more attempts, more breakthrough inertia thinking, no tools can make tools, no methods can create methods, many times, need to take the step of daring to think and dare to do.