【JST-041】One-on-one assistance office for the maintenance of mechanical and electrical equipment

This post was last edited by lizhenpeng on 2012-4-5 08:19 at http://bbs.hcbbs.com/thread-982182-1-1.html. It discusses the single-table alignment method using graph paper when aligning couplings; please include diagrams and explanations in detail. (Forum moderator’s note: Refer to the information on floor 3 for answers.)

Hello: I’ll send you a file for you to take a look at; I think it will be more helpful than me explaining it.

This post was last edited by lizhenpeng on 2012-4-17 08:54 at http://bbs.hcbbs.com/forum.php?m...18268&page=1&extra= Seeking an explanation for the cause of cavitation in centrifugal pumps (Forum moderator’s tip: Refer to answer on page 5)

This post was last edited by tjdxz on 2012-4-6 at 10:16. Cavitation and Suction Characteristics of Centrifugal Pumps – Part 1: Cavitation in Centrifugal Pumps 1. The phenomenon of cavitation: The working principle of a centrifugal pump is that the drive unit rotates the impeller through the pump shaft, generating centrifugal force. Under this force, the liquid is forced along the blade channels toward the outlet of the impeller; the liquid is then collected by the volute and sent into the discharge pipe. The liquid gains energy from the impeller, which increases both its pressure energy and kinetic energy; it is this energy that is used to transport the liquid to the point of use. As the liquid is thrown toward the outlet of the impeller, a low pressure is created at the center of the impeller inlet. This results in a pressure difference between the liquid in the suction tank and that at the center of the impeller. Driven by this pressure difference, the liquid in the suction tank continuously flows into the impeller through the suction pipeline and the pump’s suction chamber. According to the working principle of centrifugal pumps, the fluid flow enters the impeller under the effect of the pressure difference (Pa-Pk) generated between the pressure in the suction tank (Pa) and the lowest pressure at the impeller inlet (Pk). The lower the pressure Pk at the impeller inlet, the greater the suction capacity. However, when Pk drops to a certain limit value (which is currently usually the saturated vapor pressure Pt of the liquid at its transport temperature, taken as the critical value for the liquid’s vaporization pressure), cavitation occurs. 2. Severe consequences caused by cavitation: (1) Generation of vibration and noise. (2) It affects the operating performance of the pump: When cavitation reaches a certain level, a large number of bubbles are generated, which can block the flow channels and cause significant drops in the pump’s flow rate, head, efficiency, and so on. (3) The material of the flow channel can be damaged: mainly fatigue erosion of the metal near the blade inlet. II. Suction characteristics of centrifugal pumps: 1. The basic condition for cavitation to occur in a pump is that the lowest fluid pressure at the inlet of the blades, Pk, is ≤ the saturated vapor pressure of the liquid at that temperature, Pt. 2·Effective NPSH: The excess head above the vaporization pressure that remains in the liquid flow as it moves from the suction tank, through the suction pipeline, to the pump’s inlet. Denoted by Δha. 3·Required net positive suction head of the pump: The total energy loss of the fluid flow from the pump inlet to the lowest pressure point K within the impeller, denoted as Δhr. Differences and relationships between 4·Δhr and Δha: If Δha > Δhr, the pump does not experience cavitation; if Δha = Δhr, the pump begins to experience cavitation. Δha

http://bbs.hcbbs.com/thread-984967-1-1.html Please help me label the images in this post. Thank you!

My friend is copying my pictures: lol. How does my friend make the annotations? What software is used?

Bro, the pictures you took are great; I’d like to use them here. You can use Windows’ built-in Paint software to add captions – they’re available in the attachment. Thanks!

This post was last edited by lizhenpeng on 2012-4-17 08:55. I would like to ask the expert: are the rotary joints of the sodium silicate rollers in these pictures the same? What type is it? What’s its name in the market? (Publisher’s note: Refer to answer on floor 11 for reference)

It seems to be a Q-type rotary joint. Structural features of the Q-type rotary joint: The outer tube is directly connected to the roller or dryer drum; it is the precisely machined spherical surface of the main rotating component. The bottom cover and the impregnated graphite spherical seal ring together form a dynamically sealed friction pair with reliable sealing performance. The spherical seal ring slides within the annular space inside the housing, and together with the tight fit between the oil-free bearing and the housing, this allows the rotary joint to be supported freely; as a result, high precision in installation is not required. When the spherical seal ring wears out, its wear can be compensated for at any time thanks to the pre-pressure exerted by the spring. During compensation, the housing moves slowly backward, and the degree of wear of the seal element can be observed through the scale markings on the outer tube. When steam, water, or other fluids flow past the spherical seal ring and the oil-free bearing, a very thin film of liquid is formed, which provides sealing and lubrication, thereby reducing friction and wear and extending the service life. 　　 Application range:
Maximum pressure: 1.8 MPa
Maximum temperature: 220°C
Applicable media: saturated steam, superheated steam, superheated water
Sealing materials: graphite ball rings, graphite column rings, PTFE rings
Auxiliary springs: carbon steel springs
Maximum rotational speed: 100 r/min

QD/QD-F
Structural features: The outer tube is directly connected to the roller or dryer drum; it consists of a precisely machined spherical surface that serves as the main rotating component. The bottom cover and the impregnated graphite spherical seal ring together form a dynamically sealed friction pair with reliable sealing performance. The spherical seal ring slides within the annular space inside the housing, and together with the tight fit between the oil-free bearing and the housing, this allows the rotary joint to be supported freely; as a result, high precision in installation is not required. When the spherical seal ring wears out, its wear can be compensated for at any time thanks to the pre-pressure exerted by the spring. During compensation, the housing moves slowly backward, and the degree of wear of the seal element can be observed through the scale markings on the outer tube. When steam, water, or other fluids flow past the spherical seal ring and the oil-free bearing, a very thin film of liquid is formed, which provides sealing and lubrication, thereby reducing friction and wear and extending the service life. Additionally, the housing is supported by dual lugs to provide more stable support for large-scale rotary joints. The sealing is more stable. 　　 QS-Y/25 Rotating Joint for Dyeing and Printing Applications. The QS-Y(M36*4) rotating joint for dyeing and printing applications is specifically designed and improved to meet the requirements of this industry; its performance is fully equivalent to that of the older TM308 model, making it an ideal product for upgrading in the dyeing and printing sector. According to user needs, there are siphon hoses and rigid pipes inside, while specialized metal hose connectors are available outside.