A self-priming pump group that uses diesel exhaust gas to obtain vacuum
Abstract: This paper introduces a diesel engine self-priming pump unit that uses the exhaust gas flow from the diesel engine to obtain vacuum, including centrifugal pump, diesel engine, clutch, venturi tube, muffler, exhaust pipe, etc. The output shaft of the diesel engine is composed of clutch and coupling. The muffler is connected with the input shaft of the centrifugal pump, and a gate valve is installed at the exhaust port of the muffler of the diesel engine; an exhaust pipe is additionally arranged on the side of the muffler, and the exhaust pipe is connected to the air inlet of the venturi pipe, and the side of the venturi pipe The road interface is connected with the exhaust port of the pump chamber of the centrifugal pump, a gate valve and a vacuum one-way valve are installed on the pipeline, and an outlet pipe is connected to the exhaust port of the venturi tube. The exhaust gas discharged from the diesel engine is discharged into the venturi tube, and the gas in the pump chamber of the centrifugal pump and the water inlet pipeline of the centrifugal pump is pumped out to form a vacuum, so that the water lower than the water inlet of the centrifugal pump is sucked into the pump chamber to realize normal drainage.
The diesel engine pump unit is a water supply pump unit powered by a diesel engine, which is widely used in drainage, agricultural irrigation, fire protection and temporary water transfer. Diesel engine pumps are often used in conditions where water is drawn from below the water inlet of the water pump. At present, the following methods are often used for pumping water in this condition:
01、 Install a bottom valve at the end of the inlet pipe of the water pump in the suction pool: before the diesel engine pump set is started, fill the water pump cavity with water. After the air in the pump chamber and the water inlet pipeline of the water pump is drained, start the diesel engine pump set to achieve normal water supply. Since the bottom valve is installed at the bottom of the pool, if the bottom valve fails, maintenance is very inconvenient. Moreover, for a large-flow diesel engine pump set, due to the large pump cavity and the large diameter of the water inlet pipe, a large amount of water is required, and the degree of automation is low, which is very inconvenient to use.
02、 The diesel engine pump set is equipped with a diesel engine vacuum pump set: by first starting the diesel engine vacuum pump set, the air in the pump chamber and the water inlet pipeline of the water pump is pumped out, thereby generating a vacuum, and the water in the water source enters the water pump inlet pipeline and the pump chamber under the action of atmospheric pressure. Inside, restart the diesel engine pump set to achieve normal water supply. The vacuum pump in this water absorption method also needs to be driven by a diesel engine, and the vacuum pump needs to be equipped with a steam-water separator, which not only increases the occupied space of the equipment, but also increases the equipment cost.
03 、The self-priming pump is matched with the diesel engine: the self-priming pump has low efficiency and large volume, and the self-priming pump has a small flow and low lift, which cannot meet the requirements of use in many cases. In order to reduce the equipment cost of the diesel engine pump set, reduce the space occupied by the pump set, expand the use range of the diesel engine pump set, and make full use of the exhaust gas generated by the diesel engine running at high speed through the Venturi tube [1], the centrifugal pump cavity and the centrifugal pump enter The gas in the water pipeline is discharged through the suction interface of the venturi tube connected to the exhaust port of the centrifugal pump pump chamber, and a vacuum is generated in the pump chamber of the centrifugal pump and the water inlet pipeline of the centrifugal pump, and the water in the water source lower than the water inlet of the centrifugal pump is at Under the action of atmospheric pressure, it enters the water inlet pipeline of the water pump and the pump cavity of the centrifugal pump, thereby filling the water inlet pipeline of the centrifugal pump and the pump cavity of the centrifugal pump, and then starts the clutch to connect the diesel engine with the centrifugal pump, and the centrifugal pump starts to realize normal water supply.
二: the working principle of the Venturi tube
Venturi is a vacuum obtaining device that uses fluid to transfer energy and mass. Its common structure is shown in Figure 1. It consists of a working nozzle, a suction area, a mixing chamber, a throat and a diffuser. It is a vacuum generator. The main component of the device is a new, efficient, clean and economical vacuum element that uses a positive pressure fluid source to generate negative pressure. The working process of obtaining vacuum is as follows:
01 、The section from point 1 to point 3 is the acceleration stage of the dynamic fluid in the working nozzle. The higher pressure motive fluid enters the working nozzle of the venturi at a lower velocity at the working nozzle inlet (point 1 section). When flowing in the tapered section of the working nozzle (section 1 to section 2), it can be known from fluid mechanics that, for the continuity equation of incompressible fluid [2], the dynamic fluid flow Q1 of section 1 and the dynamic force of section 2 The relationship between the flow rate Q2 of the fluid is Q1=Q2，
Scilicet A1v1= A2v2
In the formula, A1, A2 – the cross-sectional area of point 1 and point 2 (m2);
v1, v2 — the fluid velocity flowing through the point 1 section and the point 2 section, m/s.
It can be seen from the above formula that the increase of the cross section, the flow velocity decreases; the reduction of the cross section, the flow velocity increases.
For horizontal pipes, according to Bernoulli’s equation for incompressible fluids
P1+（1/2）*ρv12=P2+(1/2)ρv22
In the formula, P1, P2 – the corresponding pressure at the cross-section of point 1 and point 2 (Pa)
v1, v2 — fluid velocity (m/s) flowing through the section at point 1 and point 2
ρ — density of fluid (kg/m³)
It can be seen from the above formula that the flow velocity of the dynamic fluid increases continuously and the pressure decreases continuously from the point 1 section to the point 2 section. When v2>v1, P1>P2, when v2 increases to a certain value (can reach the speed of sound), P2 will be less than one atmospheric pressure, that is, negative pressure will be generated at the section at point 3.
When the motive fluid enters the expansion section of the working nozzle, that is, the section from point 2 to the section at point 3, the velocity of the motive fluid continues to rise, and the pressure continues to drop. When the dynamic fluid reaches the outlet section of the working nozzle (section at point 3), the velocity of the dynamic fluid reaches the maximum and can reach supersonic speed. At this time, the pressure at the section at point 3 reaches the minimum, that is, the vacuum degree reaches the maximum, which can reach 90Kpa.
02.、The section from point 3 to point 5 is the mixing stage of the motive fluid and the pumped fluid.
The high-speed fluid formed by the dynamic fluid at the outlet section of the working nozzle (section at point 3) will form a vacuum area near the outlet of the working nozzle, so that the suctioned fluid near the relatively high pressure will be sucked under the action of the pressure difference. into the mixing room. The pumped fluid is sucked into the mixing chamber at the point 9 section. During the flow from the point 9 section to the point 5 section, the speed of the pumped fluid increases continuously, and the pressure continues to drop to the power during the section from the point 9 section to the point 3 section. The pressure of the fluid at the outlet section of the working nozzle (point 3).
In the mixing chamber section and the front section of the throat (section from point 3 to point 6), the motive fluid and the fluid to be pumped begin to mix, and the momentum and energy are exchanged, and the kinetic energy converted from the pressure potential energy of the motive fluid is transferred to the pumped fluid. fluid, so that the velocity of the dynamic fluid gradually decreases, the velocity of the sucked body gradually increases, and the two velocities gradually decrease and approach. Finally, at the point 4 section, the two speeds reach the same speed, and the throat and diffuser of the venturi are discharged.
三: The composition and working principle of the self-priming pump group that uses the exhaust gas flow from the diesel engine to obtain a vacuum
Diesel engine exhaust refers to the exhaust gas emitted by a diesel engine after burning diesel oil. It belongs to exhaust gas, but this exhaust gas has a certain amount of heat and pressure. After testing by relevant research departments, the pressure of the exhaust gas discharged from a diesel engine equipped with a turbocharger [3] Can reach 0.2MPa. From the perspective of efficient use of energy, environmental protection and reduction of operating costs, it has become a research topic to utilize the exhaust gas discharged from the operation of the diesel engine. The turbocharger [3] utilizes the exhaust gas discharged from the operation of the diesel engine. As a power running component, it is used to increase the pressure of the air entering the cylinder of the diesel engine, so that the diesel engine can be burned more fully, so as to improve the power performance of the diesel engine, improve the specific power, improve the fuel economy and reduce the noise. The following is a kind of use of the exhaust gas discharged from the operation of the diesel engine as the power fluid, and the gas in the pump chamber of the centrifugal pump and the water inlet pipe of the centrifugal pump is sucked out through the venturi tube, and the vacuum is generated in the pump chamber of the centrifugal pump and the water inlet pipe of the centrifugal pump. Under the action of atmospheric pressure, the water lower than the water source of the inlet of the centrifugal pump enters the inlet pipeline of the centrifugal pump and the pump cavity of the centrifugal pump, thereby filling the inlet pipeline and the pump cavity of the centrifugal pump, and starts the centrifugal pump to achieve normal water supply. Its structure is shown in Figure 2, and the operation process is as follows:
As shown in Figure 2, the water inlet of the centrifugal pump is connected to the pipeline submerged in the pool below the water pump outlet, and the water outlet is connected to the water pump outlet valve and pipeline. Before the diesel engine runs, the water outlet valve of the centrifugal pump is closed, the gate valve (6) is opened, and the centrifugal pump is separated from the diesel engine through the clutch. After the diesel engine starts and runs normally, the gate valve (2) is closed, and the exhaust gas discharged from the diesel engine enters the venturi pipe through the exhaust pipe (4) from the muffler, and is discharged from the exhaust pipe (11). In this process, according to the principle of venturi tube, the gas in the pump chamber of the centrifugal pump enters the venturi tube through the gate valve and the exhaust pipe, and is mixed with the exhaust gas from the diesel engine and then discharged from the exhaust pipe. In this way, a vacuum is formed in the pump cavity of the centrifugal pump and the water inlet pipeline of the centrifugal pump, and the water in the water source lower than the water inlet of the centrifugal pump enters the pump cavity of the centrifugal pump through the water inlet pipe of the centrifugal pump under the action of atmospheric pressure. When the pump cavity of the centrifugal pump and the water inlet pipeline are filled with water, close the gate valve (6), open the gate valve (2), connect the centrifugal pump with the diesel engine through the clutch, and open the water outlet valve of the centrifugal pump, so that the diesel engine pump set starts to work normally. water supply. After testing, the diesel engine pump set can suck water 2 meters below the inlet pipe of the centrifugal pump into the pump cavity of the centrifugal pump.
The above-mentioned diesel engine self-priming pump group using the exhaust gas flow from the diesel engine to obtain a vacuum has the following characteristics:
1. Effectively solve the self-priming capacity of diesel engine pump set;
2. The Venturi tube is small in size, light in weight and compact in structure, and its cost is lower than that of common vacuum pump systems. Therefore, the diesel engine pump set of this structure saves the space occupied by the equipment and the installation cost, and reduces the engineering cost.
3. The diesel engine pump set of this structure makes the use of the diesel engine pump set more extensive and improves the use range of the diesel engine pump set;
4. The Venturi tube is easy to operate and easy to maintain. It does not require full-time personnel to manage it. Since there is no mechanical transmission part, the noise is low and no lubricating oil needs to be consumed.
5. The Venturi tube has a simple structure and a long service life.
The reason why the diesel engine pump set of this structure can suck in the water lower than the water inlet of the centrifugal pump, and make full use of the exhaust gas discharged from the operation of the diesel engine to flow through the core component Venturi tube at a high speed, makes the diesel engine pump set that does not have the self-priming function originally. With self-priming function.
四: Improve the water absorption height of the diesel engine pump set
The diesel engine self-priming pump set described above has a self-priming function by using the exhaust gas discharged from the diesel engine to flow through the Venturi tube to obtain a vacuum. However, the power fluid in the diesel engine pump set with this structure is the exhaust gas discharged by the diesel engine, and the pressure is relatively low, so , the resulting vacuum is also relatively low, which limits the water absorption height of the centrifugal pump and also limits the use range of the pump set. If the suction height of the centrifugal pump is to be increased, the vacuum degree of the suction area of the Venturi tube must be increased. According to the working principle of the Venturi tube, to improve the vacuum degree of the suction area of the Venturi tube, the working nozzle of the Venturi tube must be designed. It can become a sonic nozzle type, or even a supersonic nozzle type, and also increase the original pressure of the dynamic fluid flowing through the venturi.
To increase the original pressure of the Venturi motive fluid flowing in the diesel engine pump set, a turbocharger can be installed in the exhaust pipe of the diesel engine [3]. Turbocharger [3] is an air compression device, which uses the inertial impulse of exhaust gas discharged from the engine to push the turbine in the turbine chamber, the turbine drives the coaxial impeller, and the impeller compresses the air. Its structure and working principle are shown in Figure 3. . The turbocharger is divided into three types: high pressure, medium pressure and low pressure. The output compressed gas pressures are: high pressure is greater than 0.3MPa, medium pressure is 0.1-0.3MPa, low pressure is less than 0.1MPa, and the compressed gas output by the turbocharger is pressure is relatively stable. If the compressed gas input by the turbocharger is used as the Venturi power fluid, a higher degree of vacuum can be obtained, that is, the water absorption height of the diesel engine pump set is increased.
五： conclusions: The diesel engine self-priming pump group that uses the exhaust gas flow from the diesel engine to obtain a vacuum makes full use of the high-speed flow of the exhaust gas, the venturi tube and the turbocharging technology generated during the operation of the diesel engine to extract the gas in the pump cavity and the water inlet pipe of the centrifugal pump. A vacuum is generated, and the water lower than the water source of the centrifugal pump is sucked into the water inlet pipe and pump cavity of the centrifugal pump, so that the diesel engine pump group has a self-priming effect. The diesel engine pump set of this structure has the advantages of simple structure, convenient operation and low cost, and improves the use range of the diesel engine pump set.