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(FAQ)Frequently Asked Questions about Chemical Pumps

Time: 2017-08-25


1.Question:How to prevent evacuation, cavitation phenomenon in operation?

 A: Take the air empty: if the pump has gas and liquid, the pump can not work, the flow and pressure tend to zero. Cavitation: is occurring in the pump during operation, from the medium within the pump, flow and pressure changes and fall, resulting in hydraulic shock. Usually take the air empty out of the pump is caused by a phenomenon in the pump, due to the installation of technical pipeline leakage, inhalation of gas caused by the evacuation has been rare, most of them are due to changes in operation and process caused. In order to avoid or control the occurrence of cavitation, in the operation of the pump flow to moderate, to minimize the pressure and the temperature can not appears to be greater change. In the pump suction line should prevent the gas from staying, the inlet pressure is negative pressure of the standby pump inlet should be closed. 


2.What is the dynamic match, static with? What is the difference between them?

1)dynamic match :the actual size of the hole is larger than the actual size of the pump

2) static fit: the actual size of the shaft is greater than the actual size of the hole formed by the match;

3) obvious difference: dynamic fit, the axis of the pair; the actual size of the hole is greater than the actual size of the hole; Hole can do relative movement; static fit: axis and the hole does not occur relative movement. 


3.What are the four basic requirements for equipment maintenance?

A: Tidy, clean, lubricated and safe 


4.What is the working principle of the labyrinth seal?

A: Labyrinth seal: there are a number of arranged in order of ring seal teeth, teeth and the rotor to form a series of throttling gap and expansion of space, the fluid through many twists and turns of the channel, after repeated throttling and produce great resistance, So that the fluid is difficult to leak, to seal the purpose. 


5.What is the interchangeability of parts? What is the main effect?

 A: 1) parts can be used to exchange each other, and to achieve the original parts of the indicators, called parts interchangeability.

2) played a mainly easy to repair, reduce maintenance time, improve equipment utilization and the role of efficiency.


6.What is a power pump?

A: power pump continuously send energy to be liquid, make its speed kinetic energy and pressure increase, who are mainly speed increases, then its speed is reduced, can make the most of the kinetic energy into pressure, use has increased the liquid to be delivered after pressure to transportation, such as: 1) the vane pump, it consists of a centrifugal pump, mixed flow pump, axial flow pump, vortex pump, etc; 2) jet pump, including gas jet pump, liquid jet pump, etc.


7.What is a Positive displacement pump?

 A: Answer: positive displacement pump in the process of periodically change the pump cavity volume, in order to function and the periodical change of displacement transfer ability to be transported liquid, so the pressure rise directly to the pressure required to achieve value after delivery, such as: 1) the reciprocating pump, piston pump, plunger pump, diaphragm pumps, extrusion, etc; 2) rotor pump, including gear pump, screw pump, rotz pump, rotary piston pump, slide pump, crankshaft pump, flexible rotor pump, peristaltic pump, etc.


8.What are the main performance parameters of centrifugal pump, motor pump?

A: mainly include: flow, head, NPSH, speed,rotor power and efficiency and so on.

9.Why do you need a regular disk drive for spare equipment? What should we pay attention to?

Answer: 1) regular disk drive for spare equipment, one is to check whether the equipment is flexible and whether there is card resistance; The second is to prevent bearing deformation and so on, really play a standby role. 2) attention should be paid to: one is that the stop position of the rotor after the plate is 180 degrees from the original position; The second part is to lubricate the lubricating oil of the pump should be oil, After turning car, to prevent damage bearing.


10.What is the hazard of the rated current over a horizontal pump?

A: The rated current is the motor in the rated voltage, rated power in the case of normal work of the current, if more than the rated current, the motor is easy to overheat, relay protection device action, so that the pump parking, such as relay protection device is not action or action Easy to burn the motor, damage the centrifugal pump.


11.What are the main contents of the pump machine inspection? 

Answer: 1) check whether the indicator of the pressure gauge or ammeter is in the prescribed area and is stable; 2) check whether the running sound is normal and there is no noise; 3) whether the temperature of bearing and motor is normal (not exceeding 60 degrees); 4) check whether the cooling water is unblocked, the packing pump, mechanical seal leakage, such as whether the leakage is within the allowable range; 5) check whether the joint site is tight and whether the anchor bolt is loose; 6) check whether the lubrication is good and the oil level is normal.



12.What should the operator of the installation work when the maintenance personnel are in service?

A) 1) Check whether the service ticket is in line with the actual equipment number of the equipment to be repaired; 2) Contact the monitor to find the power outage; 3) Provide equipment damage and repair the specific parts to the maintenance personnel; 4) Maintenance and supervision of the quality of maintenance; 5) after the completion of maintenance, contact the power supply, test; 6) after the normal operation, to monitor the duty monitor, and make a record.


13.What is the role of pump inlet and outlet valves?

A) 1) pump inlet valve is the maintenance of the pump when the pump is isolated or cut off the system components, can not be used to adjust the flow should be fully open;

 2) the outlet valve is to adjust the flow and open or shut down the pump when the system isolation Of the parts.


14.Chemical process pump according to what choice of seal?

 A: According to the process conditions and working pressure, the medium corrosion condition rotation speed selection.


15.What are the types of flat gasket seals?

 Answer: 1) non-metal cushion seal; 2) non-metal and metal composite gasket seals; 3) metal cushion seal.


16.What are the main reasons for the gasket leak?

 A: 1) leakage caused by design; A flange and flanged cover are not selected properly; B gasket selection is not appropriate; C flange and bolt materials are not selected。

 2) leakage caused by manufacturing, installation and operation; A flange and gasket machining accuracy do not meet the technical requirements; B tighten bolts, improper operation, causing gasket deviation; C flange seal face is not clean or has impurity.


17.What is mechanical seal?

Answer: mechanical seal, also called face is by at least a pair of end face of vertical axis rotation, in under the action of fluid pressure and compensation mechanism, make the two ends together, and the relative sliding and prevent fluid leak device.


18.How many types of seals are commonly used in machine pumps?

Answer: there are two kinds, dynamic seal and static seal.


19.What are the main causes of mechanical seal leakage?

 A: 1) the sealing end of the moving ring and the static ring is too worn and the loading coefficient is not reasonable in the design. so that the sealing end surface can produce cracks, deformation and breakage. 2) defects in several auxiliary sealing rings or defects due to improper assembly, and selection of auxiliary seals unsuitable for working medium. 3) spring pre-tightening force not enough or after long time operation, fracture, corrosion, relaxation, coking, as well as the working medium of crystallization suspended particles or long time accumulation of congestion in spring clearance, cause spring failure, compensation seal ring can't float, leak; 4) because the vertical deviation of the sealing end and axis of the static ring seal is too large, the sealing end of the sealing face is not tight enough to cause the leakage; 5) because the axial direction of the shaft is large, the parts associated with the seal are not well matched or the quality is poor, which is prone to leakage.


20.What material about mechanical seal friction should be selected?

Answer: according to the nature of the medium, work pressure, temperature, sliding speed and other factors to choose, sometimes also consider the ability of short time dry friction when starting or breaking the membrane.

21. What are the effective ways in which labyrinth seals increase resistance to media? 

Answer: 1) reduce clearance, 2) strengthen eddies, 3) increase the number of sealed teeth, 4) try to convert the kinetic energy of the airflow into heat energy


22. What is the working principle of floating ring seals?

Answer: the floating ring seal is based on the throttling effect produced in the narrow gap between the axis and the floating ring, and the sealing oil that is above the gas pressure is injected in the clearance to achieve the purpose of sealing the gas.


23. What is the reason for the increase in the leakage of the buy?

 Answer: 1) long-term use of floating ring, normal wear and tear, increase gap; 2) the shaft lining of the floating ring hole is rough and the accuracy is low. 3) improper assembly causes deflection, and the attachment of the middle attachment is lost, so that the oil flow is flowing out from other gaps, which is the increase of leakage;


24.What is the role of oil shield? How to conduct oil gap measurement and adjustment? 

Answer: 1) the function of oil block is to prevent bearing oil from running along the axial neck to the outside of the bearing, and there are two types of installation position: one is on the bearing pedestal and the other is on the axle. 2) oil retaining clearance can be measured by measuring ruler when oil block is disassembled or assembled. In the face of the oil gap between the axle, it can be properly relaxed. In the face of the oil gap between the bearing blocks, the requirement is strict. The lower part is 0.05-0.10mm, and the two sides are 0.10-0.20mm, and the upper part is 0.20-0.25 mm.


25. What factors influence the labyrinth seal?

A: 1) the gap between the radial clearance is too large, or the gap between the newly replaced air seal ring is too small; 2) seal or gas seal ring, between the teeth because of wear and dull, or because of long wear after the deformation of heat, resulting in the failure to use; 3) after using for a long time, the spring slacken, deformation, quickly sealing ring can not reach the designated position, after operation, precipitation accumulation of dust, dirt, is sealing medium pressure is lower than the working medium pressure and pressure instability, etc.


26.What are the common types of moving seals?

 Answer: leather bowl seal, ring seal, screw seal, pneumatic seal, hydraulic seal, centrifugal seal, packing seal, labyrinth seal, mechanical seal, etc.


27.What are the main factors that affect the seal?

 Answer: 1) seal itself quality, 2) process operation condition, 3) assembly installation precision, 4) host precision, 5) sealing auxiliary system.


28.What are the components of mechanical seal?

 Answer: mechanical seal is composed of static ring, moving ring, compensation buffer mechanism, auxiliary seal ring and transmission mechanism. The end face of the static ring and the moving ring is perpendicular to the axis of the pump and fit together to form a rotating sealing surface. Static ring and gland, all carried out with auxiliary seal ring seal ring on the shaft, to compensate for buffering mechanism drive ring along the axial movement, stay ring and static ring end face, and the wear of sealing ring end face to compensate.


29.What are the characteristics of mechanical seal?

Answer: 1) good sealing performance, leakage of mechanical seals generally 0.01 to 5 ml/h, according to the special requirements, with special design, manufacture of mechanical seal leakage of only 0.01 ml/h, and even smaller, and the packing seal leakage for 3-80 - ml/h (according to the relevant provisions of the our country, when the diameter of axle is not greater than 50 mm means flow is equal to 3 ml/h, when the diameter of axle is 50 mm means flowis qual to 5 ml/h);

 2) long lifespan of it, usually above 8000h;

 3) small friction power, only 20% to 30% of packing seal;

 4) there is no relative motion between the shaft and the shaft sleeve and the seals, and there is no friction, and the axial and axial sleeve has a longer life;

 5) the sealing surface of the mechanical seal is perpendicular to the pump axis, and the seal can produce the displacement at any time when the pump shaft is vibrating. Therefore, the vibration can still maintain good sealing performance when it is in a certain range;

 6) mechanical seal on the role of sealing liquid pressure and spring force, keep the static/dynamic ring sealing surface, and rely on the spring force to compensate for wear, so once the deployment of appropriate, in the operation of the pump in general do not need to change often, easy to use, small maintenance workload;

 7) it can be used in high temperature, low temperature, high pressure, high speed and strong corrosion;

 8) the troubleshooting and the replacement of parts are not convenient and can only be repaired after parking;

 9) the structure is complex, the assembly accuracy is higher, the assembly and installation have certain technical requirements;

 10) high manufacturing prices.


30.What are the main characteristic parameters of mechanical seal?

Answer: 1) the diameter of axle: pump mechanical seal trunnion area generally is 6-200 - mm, special is 400 mm, the diameter of axle pump usually in strength requirement by the rounded or use collar modulation to conform to the mechanical seal standard diameter of axle;

2) speed: generally, the speed of the pump is the same, the rotational speed of the general centrifugal pump is less than or equal to 3000r/min; The high speed centrifugal pump is less than or equal to 8000r/min, and the special pump is less than or equal to 4000r/min;

3) average circumference speed of sealing surface: the circumference linear velocity of the average diameter of the sealing end surface. The average linear velocity of the sealing cover is greater for the heating and wear of the sealing surface (the friction pair). In general, the circumference of the discharge seal is less than equal to 30m/s; The circumferential speed of the applied spring stationary mechanical seal is less than 100 meters per second. Special can be less than or equal to 150m/s;

4) the face ratio pressure: the end face is the contact pressure (MPa) under the sealing surface. The end face of the sealing face should be controlled within a reasonable range, and the sealing performance will be reduced by the oversize, and the sealing cover will be heated and worn by the general assembly. Mechanical seal of pump is the reasonable end surface ratio pressure value: built-in mechanical seal, generally Pc = 0.3-0.6mpa; For external loading, Pc = 0.15-0.4mpa. Better lubricity when face specific pressure can be appropriately increased, the high viscosity of liquid film increases end face specific pressure, avalible Pc = 0.5 -0.7 MPa fluid of low volatile, lubricity should take smaller end face specific pressure, good available = 0.3-0.3 MPa.

 Shanghai Shuangbao Machinery Co., Ltd.


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