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Performance characteristics of leak-free annular diaphragm pumps

19 Apr 2022Email

The annular diaphragm pump is first distinguished from the general rotor pump and the reciprocating diaphragm pump by the plane peristaltic rigid support ring and the annular diaphragm. In addition, the existing diaphragm pumps mostly use sheet diaphragms to separate the conveying medium and the working medium, and use a reciprocating crank connecting rod mechanism, a three-valve mechanism, and an inlet and outlet valve group; the annular diaphragm pump absorbs the hose pump, flexible lining ring The characteristics of the pump and other rotor pumps are the novel structure of the organic combination of the rotary drive mechanism and the annular diaphragm. The annular diaphragm pump is mainly composed of pump body 1, isolation mechanism 2, rigid support ring 3, annular diaphragm 4, bearing sleeve 5, bearing 6, transmission shaft 7, floating pressure bearing ring, pump end cover, etc.; The cover is pressed and fixed in the axial direction, and it forms a closed volume with the pump end cover, the rigid support ring and the pump body. When the transmission shaft rotates, the suction and discharge chambers are formed with the help of the inlet and outlet isolation mechanisms, the rigid support ring and the pump body. , to achieve the purpose of conveying the medium without leakage.

 

 

The main structural features of the annular diaphragm pump are:

(1) There is a plane peristaltic rigid support ring between the diaphragm and the pump body;

(2) The annular diaphragm has a built-in floating pressure ring;

(3) The annular diaphragm separates the conveying medium from the lubricating medium;

(4) The annular diaphragm pump has a unique combination of inlet and outlet isolation mechanism;

(5) No bottom valve and inlet and outlet valve groups are required;

(6) Unique axial sealing structure;

(7) Bearings are provided between the rigid support ring and the transmission shaft.

 

1. Traffic

In the annular diaphragm pump, the rigid support ring, the isolation element and the pump body separate the liquid cavity into the suction and discharge parts. With the change of the volume of the suction and discharge liquid cavity, the medium flows continuously from the inlet to the outlet. As shown in Figure 2, the suction port A and the discharge port B are the radial sealing dead points of the suction and discharge chambers, respectively. It can be seen that the theoretical discharge flow per revolution should be:

Q;, t=10-'n(RZ-r2)BK[L]

In the formula, B--the width of the rigid support ring, cm

R--radius of pump body cavity, cm

r--radius of rigid support ring, cm

K--theoretical volume coefficient, mainly considers the influence of invalid sealing angle α and structural dimensions R, r, etc. on the theoretical flow; usually, the invalid sealing angle α is controlled at 20 respectively. Within the range, the K value can be obtained accurately, generally taking 0.90-0.95. There is R=r+e in the design, where e is the eccentricity value, cm. Then the theoretical flow rate of the pump is: considering the influence of the pressure difference of the pump, the viscosity of the medium, the size of the gap and the pump speed on the flow rate, the rated flow rate of the pump is:

Qr=KvQth

In the formula Kp--volume coefficient

2.2. Determination of pump speed and pump radial and axial clearance

2.2.1. Pump speed

Since the rigid support ring with plane peristalsis is used, the relative sliding speed between the pump body, the pump end cover and the rigid support ring is related to the pump speed, and its value can be estimated, namely:

V=πne/30

It can be seen that reasonable control and reduction of pump speed can reduce friction and power loss, prolong pump service life and improve pump efficiency. According to experience, the pump speed is usually controlled within the range of n≤300min-1.

 

2. Shaft, radial clearance

The radial seal between the suction and discharge chambers is a wedge-shaped gap, and the axial gap is a parallel gap. The performance of the pump is closely related to the radial and axial clearances and related structural parameters and medium characteristics. The radial clearance is mainly determined by the pressure difference ΔP; the viscosity of the conveying medium γ; the radius of the rigid support ring r; the eccentricity value e and other factors.

That is, the gap T=f(ν,r)/f(△P,e). Obviously, when △P and e increase, the gap T should take a small value; when ν, r increase, the gap T can take a large value.

The axial seal uses a combination of gap seal and elastic seal, and the leakage of the parallel gap can be estimated by the following formula:

q=10-5xT3b△P/1.2γL[mL/s]

where b-gap width, cm

L-gap length, cm

△P-pressure difference, MPa

ν-dynamic viscosity of medium, Pa s

T-gap value, cm

Usually, reasonable control of diameter and axial clearance can improve the self-priming performance and discharge pressure, reduce the leakage in the pump, and maintain a high volume coefficient. Practice has proved that the calculation of the tolerance fit, radial and axial dimension chains of the rigid support ring and the pump body, the drive shaft and the bearing sleeve, and the bearing and the bearing cover is very important. Through design analysis and test verification, the radial and axial clearances should be controlled within the range of 0.03 to 0.20.

 

3. Design of annular diaphragm

The annular diaphragm is a key part in the annular diaphragm pump that separates the conveying medium and the lubricating medium and realizes leakage-free conveying of the medium. Its design is different from the sheet diaphragm. We ensure that it can withstand low pressure from the structure, and make it work through a predetermined amount of elongation. The additional deformation in the state is extremely small, and the following principles are followed in the design:

(1) There is no relative sliding friction on the inner and outer surfaces of the annular diaphragm;

(2) Control the pressure difference between the inner and outer surfaces of the diaphragm within 0.1MPa;

(3) Using a floating bearing ring to form a floating support;

(4) Improve the tensile and fatigue resistance of the diaphragm;

(5) Reasonable selection of diaphragm hardness;

(6) Ensure that the diaphragm is easy to assemble and disassemble;

(7) The pre-elongation value △L of the diaphragm is given.

If the size of the working deformation section of the annular diaphragm is L, and the installation size is L', then the design length of the annular diaphragm is:

L=△L+L'

where △L=e/sin(arctge/L)-L

Usually △L=0.5-2.0mm, considering that although the annular diaphragm is low in pressure, it is in contact with corrosive media and the cyclic vibration during operation and the strict structural size requirements. Rubber, polyurethane rubber and natural rubber and other diaphragms, the physical and chemical properties and fatigue properties of the polyurethane diaphragm are better through comparative tests.

 

4. Design of rigid support ring

The rigid support ring in annular diaphragm pump is different from ordinary rotor pump and reciprocating diaphragm pump. Its setting not only makes the axial and radial seals easy to form, but also protects the diaphragm and ensures that the pump has high discharge pressure and good self-priming performance.

The motion of any particle on the rigid support ring is the plane motion synthesized by the reciprocating motion and the rotary motion in the vertical axis section, that is, plane peristalsis. The design of the rigid support ring should consider the use of lightweight materials or hollow structures to reduce weight and reduce inertial forces.

Under its working state, the outer surface is subjected to unbalanced hydraulic pressure, so that the transmission shaft is subjected to radial force F. When the radial sealing point is far away from the lowest point of the combined isolation mechanism, the following formula is obtained:

Fmax=20·△P·B·r

In the formula △P-pressure difference, MPa

B- Rigid support ring width, cm

r-radius of rigid support ring, cm

It can be seen from the above formula that the rigid support ring bears a large radial force, so in the design, not only should it ensure sufficient rigidity and strength, but also the possible deflection of the transmission shaft should be considered, and the radial clearance of the pump should be ensured through the structural design. within the range.

 

Performance characteristics

The annular diaphragm pump has excellent performance with unique structure, optimized design, reasonable matching of parameters and high-quality diaphragm, mainly as follows:

(1) No leakage. Because the annular diaphragm in the pump separates the conveying medium from the lubricating medium, the conveying medium cannot escape.

(2) Strong self-priming performance. Because it is a rotary positive displacement pump, it has better self-priming ability, and can be mixed with oil, gas and water, and the pump can be started directly without irrigation.

(3) Wide range of adaptation. It can transport general liquids and viscous media, and has a wide range of application parameters.

(4) High efficiency. The transmission structure is compact and simple. Compared with the vane pump with the same parameters, the efficiency is more than 5% higher, and the high-efficiency area is wide.

The product is easy to be serialized and generalized; the same base product can replace the overflow parts, adjust the pump speed and clearance to adapt to different working conditions and media. At present, the annular diaphragm pump has formed a series of products with Q=1~50m3/h, P≤1.0MPa, which can be widely used for conveying highly corrosive, flammable, explosive, highly toxic and radioactive as well as high-purity or high-viscosity media, etc. . In addition, according to the requirements of different users, the speed-adjustable transmission mode can be adopted, and the diaphragm alarm automatic actuator can also be used.

 

5. Product rigidity

According to the identification requirements of the "Development of Annular Diaphragm Pumps for Military Ships", the performance of the two products is shown in Table 1 after 500h type test.

It can be seen that the measured performance of the product has reached the key target of the Ministry of Machinery, with good self-priming performance, gas-liquid mixed transportation, and high efficiency.

In addition, we conducted a comparative test with the HM-2.0/0.4 annular diaphragm pump, and its performance under different media and different pressure differences is shown in Table 2.

Obviously, when the viscosity and pressure difference are different, under the same sealing gap, the amount of internal leakage generated is different, which makes the volume coefficient different.

 

6. Conclusion and application

As a new type of volumetric rotor type leak-free pump, the annular diaphragm pump adopts a rotary drive mechanism, which reduces the sliding friction lubrication points and simplifies the structure. The annular diaphragm is used to separate the lubricating medium and the conveying medium, which is unique and novel. In addition, because it is fundamentally different from the reciprocating diaphragm pump, rotor pump, magnetic pump, hose pump, etc., its research and development and market application potential are great.

The annual output of non-leakage pumps in industrialized countries accounts for 15% to 20% of the annual output of pumps; while the annual output of non-leakage pumps in my country accounts for about 3% of the total output, it is a product that needs to be developed urgently. The unique performance and good versatility and interchangeability of the annular diaphragm pump make it especially suitable for the renewal of pumps used in chemical, light industry, and food industries, reducing operating costs, facilitating maintenance and operation, and improving economic benefits.

According to the investigation of pumps used in an alcohol factory and fructose factory, the two units use nearly 360 pumps to transport different media such as oil, water, alcohol, liquor, syrup, additives, etc. The pressure difference is P=0.2~0.5MPa, and the flow rate Q= 15~40m3/h; more than ten varieties and 50 specifications of products such as oil pumps, stainless steel pumps, single screw pumps, canned pumps, and clean water pumps are selected, and it is inconvenient for operation management and maintenance to replace parts. If the annular diaphragm pump series is used, only 2 bases are needed. The installation size, pump body, diaphragm and other components are the same. The material of the overflow parts can be replaced for different media, and the maintenance and management are simpler.

The pump can not only meet the needs of military ships to replace vertical electric reciprocating pumps for transporting seawater and sewage and plunger pumps used in marine oil-water separators, but also has the ability to mix gas and liquid, especially suitable for oil, gas and water in oil fields. Mixed transportation; suction of ship bilge sewage, residual oil and residual liquid at the bottom of tankers.

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