Pneumatic Pressure Monitoring and Control System

Study: Optimization of the Operation of a Double Diaphragm Pneumatic Pump and Monitoring Through a Pressure Transducer.

  • ABSTRACT

Compressed air pressure is a variable sensibly to long or poorly designed distribution networks. These variations can be decisive for the efficiency of the operation of equipment such as actuators, valves, pumps, etc. The project of this article was conceived with the purpose of controlling the pneumatic pressure of a double diaphragm pump, allowing a continuity of work even in pressure variations of the compressed air network. The article also covers other information about the components and aspects of monitoring through a pressure transducer.

  • INTRODUCTION

In motion automation in industry, energy can be used in different ways. Electric energy in its traditional forms, hydraulic energy when the need for great efforts and pneumatic energy when we need moderate effort and high speeds, when the environment requires a greater degree of cleanliness or when it is flammable or hostile.

The varied consumption of air in industrial plants, caused by machines and equipment that sometimes consume more, sometimes less, make it impossible to have compressed air in a continuous flow of pressure and flow. The compressed air networks in the industry, in a common situation, usually oscillate between 4 and 6 BAR of pressure, however in a situation of high consumption or a long distance from the compressed air generator, the pressures can reach around 2 or 3 BAR causing failures in the pneumatic systems and/or lost productivity.

  • OPERATIONAL DEFINITIONS.

The system is based on the reading and interpretation of pressure by the pressure transducer that sends the information to a programming software based on pascal.

The transducer has a working range of 0-10 BAR input with 0-10vdc output, as shown in the tables below.

RangeOutputRangeOutput
1 BAR1 vcc6 BAR6 vcc
2 BAR2 vcc7 BAR7 vcc
3 BAR3 vcc8 BAR8 vcc
4 BAR4 vcc9 BAR9 vcc
5 BAR5 vcc10 BAR10 vcc

Figure 1.

Through the software, the user enters the command data on the opening and closing pressures of the solenoid valve. With the opening of the valve, the pressure flow enters the pressure multiplier (multiplication factor 2.0) that moves its piston, increasing the pressure until reaching the pressure 2P, as shown in the graph below.

Figure 2.

The pressure multiplied by the multiplier which can also be called a booster moves to a compressed air accumulator with the following dimensions Ø125 x 450mm with a volume capacity in liters of 557.77 liters at 10 BAR of pressure.

Formula for calculating volume:

V1 = π. r². C

V1 = 3.1415. 62.5². 450

V1 = 5.522.167,9 mm²

V1 = 5,522,167.9 / 1,000,000 (mm³/liters)

V1 = 55.22 liters

Formula for calculating the volume with a pressure of 10 BAR:

V2 = (P1 . V1)/ATM

V2 = (10.55,22)/0.99

V2 = 557.77 liters with 10 BAR

Being:

V1: Volume of ar

r: Reservoir radius

C: Reservoir length

V2: pressurized volume

P1: Air pressure inside the reservoir

ATM: Local atmospheric pressure.

The multiplied and monitored pressure can be used in many applications. In the course of this article we will present some of these.

Pressure transducer

Pressure sensors are transducers that convert the physical quantity pressure into a proportional electrical signal, as shown in the following figure.

As we have seen, in this project this signal will be handled by an electronic circuit and later processed by the software in the computer.

This pressure transducer is factory calibrated, but depending on the need, it can be adjusted.

When pressure is applied, the deflection of the diaphragm (sensor) leads to changes in the implanted resistances according to the piezoresistive effect (variation of electrical resistance as a function of the applied force), thus causing a change in conductivity. Compression and expansion forces on the semiconductor crystal are used to produce changes in the resistance of piezoelectrics connected as a bridge circuit, thus varying the output voltage of the bridge according to the sensitivity specified on the transducer.

There are several models of pressure transducers, such as transducers with differential pressure tapping and also more fragile models to work with low pressure and to be used in instrumentation circuits that are not in contact with the industrial environment, such as medical equipment, for example.

STUDY: OPTIMIZATION OF OPERATION OF A DOUBLE DIAPHRAGM PUMP.

In this case study, the project objective is to maintain a peak fluid outlet pressure from the pneumatic pump greater than 50% of the available air pressure in the network. Increasing the working efficiency of the equipment.

(P)(2P)(PP)
Mains pressure (BAR)Multiplied Pressure (BAR)Peak Fluid Pressure (BAR)Fluid pressure comparison without booster
0,51(-)¹(-)¹
121,5(-)¹
243,441,5
3652,75
3,575,853
4(-)²3,44

Figure 4.

(-)¹ Pump does not operate.
(-)² Maximum supply pressure: 7 BAR

DETAILS OF THE SYSTEM COMPONENTS.

Compressed air accumulator

The main function of this accumulator will be to store compressed air so that it can feed a main device or actuator, such as a pump, pneumatic hammer, pneumatic clutch or brake, spray guns, etc. Both need an adequate amount of pressure for their proper functioning. The accumulator is powered by a pressure multiplier and monitored by a pressure transmitter sensor. Dimensions of the accumulator: Ø125 x 450mm with a capacity of 557.77 liters with 10 BAR of pressure in BAR.

pressure transmitter

The signal from the pressure transmitter sensor will be monitored by the software that will determine the maximum and minimum pressure limits for the consumption device to function. When there is a low pressure in the compressed air network, the transmitter sensor sends a signal to the relay that closes the contact of the solenoid valve, causing a passage to open, as it were, and the air to move to the multiplier of pressure, increasing it until reaching the desired level and then moving to the compressed air accumulator/tank. The pressure transmitter is a model IT-TR Velki Range 0 – 10 BAR, output 0 – 10vdc with a supply of 13-28vdc.

Pressure Multiplier or Booster

As soon as the air passes through the solenoid valve, it reaches the pressure multiplier cylinder, where the pressure of the compressed air that arrives is amplified, according to the desired regulation. So it can be multiplied up to twice its initial value. The pressure multiplier is a VBA model from SMC with a multiplication factor of 1.0 to 2.0 and a flow rate of up to 1000 L/min.

Solenoid Valve

Solenoid valve is responsible for opening and closing the flow of compressed air into the pressure multiplier, it is commanded by the relay signal that allows the start of the pneumatic system. It is a 2/2 way valve 1/2'' brass body N.F. with neoprene diaphragm and 220v solenoid coil. ACL Italy brand, E108DB12/C/10611.

Retention valve

Check valve allows the flow of compressed air in only one direction, always blocking the opposite flow. It is a 1/4″ valve with an internal ball/spring system.

Double Diaphragm Pneumatic Pump

The central block of the pump has an air valve that directs the compressed air, initially pressurizing one of the diaphragms (chamber B), which in turn drives the fluid that is in the chamber in front of it (liquid chamber). The fluid is propelled upwards, due to the action of the ball/seat assemblies, being directed to the outlet through the manifolds (manifolds), while the other diaphragm is pulled back by the shaft that interconnects the diaphragms, sucking the fluid into the another pumping chamber (chamber A). When the diaphragms complete their stroke, the valve pressurizes the chamber of the opposite diaphragm, generating the same process as described above. The pump under study is a model pump Husky 515 Graco, 1/2''. Polypropylene body, spheres, teflon accents and diaphragm, maximum flow of 61 L/min. Test fluid: Water, viscosity 1 cps, 0% solids, atmospheric pressure 0.99 ATM, fluid inlet and outlet pressure adjustable in the recirculation system.

Pressure regulator

A pressure regulator is a device constructed to regulate the pressure of a fluid, generally having a higher and variable pressure at its inlet and providing a lower and reasonably stable pressure at its outlet.

In the scheme, there are two pressure regulators ¼ maximum pressure of 10 BAR, with a maximum flow of 1100 liters at a pressure of 7 BAR.

Electronic board

The board that was made for this project consists of a hardware that reads an analog signal (0~10V) and transforms it into an electronic signal. This circuit is characterized as an A-D (analog to digital) converter. This analog value will be obtained from a pressure transducer, which will send voltage signals to the hardware, being 1V – 1 BAR, 1V – BAR, 3V – 3 BAR and so on.

When converting the signal emitted by the transducer, it will be sent directly, in binary, to the parallel port.

software programming

Using the Turbo Pascal software, and basic programming knowledge (see figure 5 for the programming lines), the signal from the control board will be read. With this data on the screen, we made an automatic control of pressure control from the digital inputs of the hardware, which has 2 relays of 12V each activated by transistors and 2 LEDs.

Figure 5 – Programming Lines.

RESULTS ANALYSIS.

After a series of tests using the devices, the transmitter operated with a satisfactory response, monitoring the following measurements, according to the table below:

Average of the Pressure verified in the analog device (BAR)Transmitter Signal (Volt)
00,58
11,55
22,48
33,55
44,55
55,55
66,55
77,55
88,58
99,5
1010,58

Figure 6.

The multiplication factor (Factor: 2.0) followed the inlet pressure with pressure increase according to the following table:

Multiplier inlet pressure (BAR)Pressure in the analog device checked at the output (BAR)pressure increase
11,7272,00%
23,6783,50%
35,5183,67%
47,792,50%
59,7494,80%

Figure 7.

Within the margin of error of analog pressure gauges and the parallax error, we can consider that the components effectively meet the objective.

As shown in the next table, the bomb obtained the following results in converting the pneumatic pressure into the peak pressure of the pumped fluid (PP)

(P)(2xP )(PP)
Mains pressure (BAR)Multiplied Pressure (BAR)Peak Fluid Pressure (BAR)
23,673,33
2,54,594,13
35,515,17

Figure 8.

Other System Applications.

The system can be perfectly used in other applications such as:

Slip mill clutch: (Fig.: 9) With the pressure drop at levels like 2 BAR, the mill's clutch chamber does not inflate enough to generate friction on the clutch lining wall and the mill starts the movement by “skidding” the tapes. This generates excessive wear.

Figure 9 – Barbotina Mill.

pneumatic brake (Fig.:10).Used in slip mill: The pneumatic brake is activated by a piston that locks the disc, when this piston has little pressure on the piston it loses strength and as a consequence the brake loses its action. Work accidents can occur if the mill moves without proper care.

Figure 10 – Pneumatic Brake.

Screen printing tensioner (Fig.:11): Used to inflate a bladder serving as a surface for the manufacture of silkscreen screens used in the ceramic industry. When the bladder pressure is not adequate, the mesh fails.

Figure 11 – Screen tensioners for screen printing.

pneumatic hammer (Fig.:12): The hammer uses minimal pressure to move its plunger pushing it against a spring with high traction that, after completing the stroke, the air is expelled and the plunger returns with great force pushing the hammer. If the pressure is low the system will not work.

Figure 12 – Pneumatic hammer vibrator.

SYSTEM IMAGES

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