Improper piping design/layout can lead to problems such as hydraulic instability and cavitation in the pump system. To prevent cavitation, focus should be placed on the design of the suction piping and suction system. Cavitation, internal recirculation and air entrainment can lead to high levels of noise and vibration, which can damage seals and bearings.

Pump Circulation Line

ពេលណា ម៉ាស៊ីនបូមករណីបំបែកផ្តេក must operate at different operating points, a circulation line may be required to return part of the pumped liquid to the pump suction side. This allows the pump to continue to operate efficiently and reliably at the BEP. Returning part of the liquid wastes some power, but for small pumps, the wasted power may be negligible.

The circulating liquid should be sent back to the suction source, not to the suction line or pump inlet pipe. If it is returned to the suction line, it will cause turbulence at the pump suction, causing operating problems or even damage. The returned liquid should flow back to the other side of the suction source, not to the suction point of the pump. Usually, appropriate baffle arrangements or other similar designs can ensure that the return liquid does not cause turbulence at the suction source.

ប្រតិបត្តិការប៉ារ៉ាឡែល

When a single large ម៉ាស៊ីនបូមករណីបំបែកផ្តេក is not feasible or for certain high flow applications, multiple smaller pumps are often required to operate in parallel. For example, some pump manufacturers may not be able to provide a large enough pump for a large flow pump package. Some services require a wide range of operating flows where a single pump cannot economically function. For these higher rated services, cycling or operating pumps away from their BEP creates significant energy waste and reliability issues.

When pumps are operated in parallel, each pump produces less flow than it would if it were operating alone. When two identical pumps are operated in parallel, the total flow is less than twice the flow of each pump. Parallel operation is often used as a last solution despite special application requirements. For example, in many cases, two pumps operating in parallel are better than three or more pumps operating in parallel, if possible.

Parallel operation of pumps can be a dangerous and unstable operation. Pumps operating in parallel require careful sizing, operation, and monitoring. The curves (performance) of each pump need to be similar - within 2 to 3 %. Combined pump curves must remain relatively flat (for pumps running in parallel, API 610 requires a head increase of at least 10% of the head at rated flow to dead center).

Horizontal Split ករណីបូម បំពង់។

Improper piping design can easily lead to excessive pump vibration, bearing problems, seal problems, premature failure of pump components, or catastrophic failure.

Suction piping is particularly important because the liquid should have the right operating conditions, such as pressure and temperature, when it reaches the pump impeller suction hole. Smooth, uniform flow reduces the risk of cavitation and allows the pump to operate reliably.

Pipe and channel diameters have a significant impact on head. As a rough estimate, the pressure loss due to friction is inversely proportional to the fifth power of the pipe diameter.

For example, a 10% increase in pipe diameter can reduce head loss by about 40%. Similarly, a 20% increase in pipe diameter can reduce head loss by 60%.

In other words, the friction head loss will be less than 40% of the head loss of the original diameter. The importance of net positive suction head (NPSH) in pumping applications makes the design of the pump suction piping an important factor.

Suction piping should be as simple and straight as possible, and the total length should be minimized. Centrifugal pumps should typically have a straight run length of 6 to 11 times the suction piping diameter to avoid turbulence.

Temporary suction filters are often required, but permanent suction filters are generally not recommended.

Reducing NPSHR

Instead of increasing the unit NPSH (NPSHA), piping and process engineers sometimes try to reduce the required NPSH (NPSHR). Since NPSHR is a function of pump design and pump speed, reducing NPSHR is a difficult and costly process with limited options.

The impeller suction orifice and the overall size of the horizontal split case pump are important considerations in pump design and selection. Pumps with larger impeller suction orifices can provide lower NPSHR.

However, larger impeller suction orifices may cause some operational and fluid dynamic problems, such as recirculation issues. Pumps with lower speeds generally have lower required NPSH; pumps with higher speeds have higher required NPSH.

Pumps with specially designed large suction orifice impellers may cause high recirculation issues, which reduces efficiency and reliability. Some low NPSHR pumps are designed to operate at such low speeds that the overall efficiency is not economical for the application. These low speed pumps also have low reliability.

Large high pressure pumps are subject to practical site constraints such as pump location and suction vessel/tank layout, which prevents the end user from finding a pump with the NPSHR that meets the constraints.

In many refurbishment/remodeling projects, the site layout cannot be changed, but a large high pressure pump is still required on site. In this case, a booster pump should be used.

A booster pump is a low speed pump with a lower NPSHR. The booster pump should have the same flow rate as the main pump. The booster pump is usually installed upstream of the main pump.

Identifying the Cause of Vibration

Low flow rates (usually less than 50% of the BEP flow) can cause several fluid dynamic problems, including noise and vibration from cavitation, internal recirculation, and air entrainment. Some split case pumps are able to resist the instability of suction recirculation at very low flow rates (sometimes as low as 35% of the BEP flow).

For other pumps, suction recirculation can occur at about 75% of the BEP flow. Suction recirculation can cause some damage and pitting, usually occurring about halfway up the pump impeller blades.

Outlet recirculation is a hydrodynamic instability that can also occur at low flows. This recirculation can be caused by improper clearances on the outlet side of the impeller or impeller shroud. This can also lead to pitting and other damage.

Vapor bubbles in the liquid flow can cause instabilities and vibrations. Cavitation usually damages the suction port of the impeller. The noise and vibration caused by cavitation can mimic other failures, but inspection of the location of pitting and damage on the pump impeller can usually reveal the root cause.

Gas entrainment is common when pumping liquids close to the boiling point or when complex suction piping causes turbulence.