Submersible sewage pump model selection

Most of the submersible sewage pumps we see on markets today call themselves non-clogging sewage pumps. But are they really non-clogging? That depends. Clients usually find their sewage pumps get clogged soon after being put into use in the sewage pool. As a result, the motor of the pump burns out.

Reliability is of key importance for sewage pump model selection. We need the sewage pump to deliver fluids that contain solid materials. That calls for higher standards for submersible sewage pump in terms of mechanical seal, motor capacity, shaft arrangement and selection, than common pumps.

To prolong the service life of submersible sewage pumps, most manufacturers at home and abroad are trying to find a solution with protective system.

It is necessary to add protective system to the submersible sewage pump. But this is not the key to the problem.

To solve the problem thoroughly, we should work on the mechanical seal and overload of the motor.

Notes for submersible sewage pump model selection

The flow quantity of submersible sewage pump should be counted by seconds. If you need to adjust the flow quantity, you can choose according to the max rated value.

We should decide the head of the pump according to the lifting height and loss in pipeline. If you need to deliver mixed fluids containing solid materials, such as sands, generally you should choose self-priming submersible sewage pump. Before placing the order, you had better get a good knowledge about the seal performance and load capacity of the pump.

Submersible sewage pumps used in buildings include submerged sewage pump, vertical submersible sewage pump and horizontal submersible sewage pump. For the last two types, we need to set a shock insulation base, which would take some ground space. For that reason, these two types are rarely used in buildings.

Two ways to lubricate the shaft bearing of submersible water pump

Oil drop from oil cup (submersible water pump):

This way of lubricating is to let oil drop onto the shaft bearing from the outlet of oil cup. Its advantages are simple structure, convenience and oil-saving. Besides, the supply amount can be adjusted through the outlet. Generally, the speed had better be 3~8 drops per second. Too much lubricating oil will make the shaft bearing rise in temperature. Its disadvantages are that the viscosity of the lubricating oil has to meet certain requirement. If it has too high viscosity, it will lose the function of dissipation. The oil drop way of lubricating is suitable for occasions where the submersible water pump rotates at low speed, with fewer load and the working temperature is low.

Oil bath or oil immersed lubricating:
This way is to immerse the shaft bearing into the lubricating oil. When the shaft bearing moves, it will bring the oil to other parts of the submersible water pump. Oil bath lubricating is one of the most common and easiest ways.

Considering about oil loss in mixing and temperature rise, for horizontal shafts, there should be a limit to the depth of shaft bearing in lubricating oil. Usually, we should keep the oil level near the center of the rolling body at bottom of the shaft bearing. With oil bath, we can thoroughly lubricate the shaft bearing. But it is not convenient to adjust the supply amount of oil. If there is no filter device, it will be easy for impurities to enter the shaft bearing and damage it. This method is usually suitable for submersible water pumps rotating at low speed or medium speed, more common for low speed shaft bearings.

According to our experience, separable reinforcing rib can be installed at the bottom of the shaft base to reduce blending or to improve dissipation. Static oil level should a little lower than the center of the rolling body of the horizontal shaft. As for vertical shaft, static oil level should cover 50%~80% of the rolling body. If the temperature of the shaft bearing is high when you use oil bath system, you can change to the oil drop method.

Six technical protective lines for a stainless steel centrifugal pump

A stainless steel centrifugal pump usually has six protective lines. They are to protect the pump from damage and keep it running normally. We should set the protective lines according to the working conditions.

1.We should set DN20-25 warm-up lines if the pump delivers high temperature oil over 200 ℃, on condition that a standby pump is available.
2.Small flow quantity line
Sometimes the working flow quantity of the stainless steel centrifugal pump is lower than the rated value by 30%. In this case, we should set a small flow quantity line when it is running with minimum flow quantity.
3.Balance line
Sometimes, the saturated vapor pressure of the fluids the stainless steel centrifugal pump delivers is higher than the atmospheric pressure at room temperature. Sometimes, the fluids are at bubble point. In these cases, in order to prevent vapor or bubble from entering the pump and causing cavitation, we should add a balance line.
4.Bypass-line
If the stainless steel centrifugal pump is taking a test run or if it is not running normally, the main valve at its outlet will close. A bypass-line can make the pump continue running in that case. Generally, in conditions where the pressure difference at two sides of the valve is large, we should set a bypass-valve with metering hole.
5.Anti-condensation line
If you use the stainless steel centrifugal pump to deliver a fluid of high freezing point under room temperature, you should set a anti-condensation line to its preparatory pump and the pipelines to prevent clogging.
6.Safety valve line
For positive displacement pumps, such as electric reciprocation pump, gear pump, screw pump, we should set a safety valve at exit. If the pressure at exit is larger than the rated value, the safety valve will bounce up. And the fluid will move back toward the entrance.
For more formation, please contact info@welpump.com.

Improve the performance of self-priming sewage pump

1.Install a suction valve at the end of the suction pipe of the self-priming sewage pump.

In fact, suction valve is a kind of check valve. It ensures that the sewage water only runs from the sewage pool to the suction pipe, not vice versa. Hence, even if the scale height of the axial line of the sewage pump is higher than the working water level of the sewage pool, the sewage water still won’t flow back. In this way, the suction pipe will always be full of water. And you can make the sewage pump start automatically and quickly.

The reliability of this way of suction depends on the quality of the suction valve. For instance, if the valve is not closed tightly, or if it leaks, the water in suction pipe will flow back. With time going on, there will be no more water in suction pipe. As a result, you have to take efforts to fill the self-priming sewage pump before starting it.

2.Self-priming sewage pump can help to reduce bends of suction pipe, shorten the height difference and horizontal distance.

3.Add a suction tank in front of the self-priming sewage pump

This is to add a suction tank to the suction pipe of the self-priming sewage pump. When the pump starts for the first time, you should fill it with water. After it stops, the suction pipe of the suction tank will be higher than the water level inside the pipe. Therefore, even though the water level of the sewage pool is higher than the water level inside the tank, the water in tank still won’t flow back to the pool.

In this way, the suction tank can hold a certain amount of water. What’s more, the outlet pipe of the suction tank, that is, the suction pipe of the self-priming sewage pump, is lower than the water level inside, which guarantees that the suction pipe of the pump will always be full of water. Next time when the self-priming sewage pump starts, the water in the suction tank will be taken away, generating negative pressure inside. While the water in sewage pool will move to the suction tank under the effect of atmosphere pressure.

Add a vacuum pump on the suction pipeline of the self-priming sewage pump.

Before the sewage pump starts, the vacuum pump will start beforehand. The vacuum pump will make the suction pipe of the sewage pump be full of water, which makes sure the sewage pump starts automatically and quickly. This method needs a well developed automatic system to ensure normal working.

How to select a mechanical seal for 18 m high head submersible pump?

Mechanical seal is an important part for a 18 m high head submersible pump. It is one of the basic mechanical parts that have precise and complex structure. It is a key component for all kinds of high head submersible pump. Its performance and service life depends on many factors. These factors are model selection, accuracy of the high head submersible pump, correct installation and operation, etc

Model selection methods:

According to different working conditions and natures of the fluids, we can divide mechanical seals to different categories. That is, high temperature or low temperature resistant mechanical seal, high pressure and corrosion resistant mechanical seal, etc. Some mechanical seal resists solid particles, while others are suitable for light hydrocarbon which are easy to vaporize. We should choose a mechanical seal with appropriate structure and material for specific application.

You need to consider five primary parameters before selecting a proper model of seal. The parameters are sealed chamber pressure (MPa), fluids temperature (℃), running speed of the high head submersible pump (m/s), fluids properties and the available space for installation.

Basic principles for model selection:

We should decide if the seal should have balanced or imbalanced structure, single end face or double end faces, according to sealed chamber pressure.

We should confirm which type of seal suits the running speed of the high head submersible pump, rotatory type or still type, hydrodynamic type or non-contact type.

The material of friction pair and auxiliary seal depends on the temperature and the nature of the fluids. Besides, we should also choose proper circulation protective systems for mechanical seal. The systems include the lubricating system, washing system, thermal insulation system and cooling system.

Based on the available space for installation, we can choose a mechanical seal of more springs, single spring or wave shaped spring, built-in type or external mounted type.

For more information, please contact info@welpump.com

Boycott fake stainless steel sewage pump

1.To boycott fake stainless steel sewage pump, we had better get a good knowledge about the steps and methods of manufacturing fake stainless steel sewage pump. 1. The fake pump makers will choose a renowned manufacturer. It doesn’t matter if this manufacture really produces any stainless steel sewage pump, as long as it is famous. The fake pump makers would like the renowned manufacturer be far from their own company. Many buyers will give up paying a visit to the agent and manufacturer because of long distance. The long distance does the fake pump makers a favor. For instance, if the faker pump makers are at the southwest, they will choose a renowned manufacturer at the northeast. In a word, to the fake pump makers, the longer the distance, the better.

2.  Next, they will register a company name that is similar to the name of the renowned manufacturer. For example, if the manufacturer’s name is Tianjin XX stainless steel sewage pump company, the agent or the fake pump maker will call themselves Shanghai XX stainless steel sewage pump company. In fact, these two companies have no relation at all. They are both independent legal person. Each of them runs their business independently and take independent responsibility. The customers and purchasers will take them as general company and branch company by mistake, thinking that they have close relations.

3. Pay management fee and take the stainless steel sewage pump

Many manufacturers are ignorant and have no foresight. Some manufacturers even boldly support the fake pump makers as they want to make profits through the management fee paid to them by the so-called agents. The renowned manufacturer will produce some models of stainless steel sewage pump. For these models, the agent will stock from the manufacturer. But for other models, the agent will get from small workshops or illegal enterprises, and put on the manufacturer’s labels and certification. These labels and certification are not from the manufacturer, but they are as authentic as the real ones. The fake labels and certificates are very cheap to make.   It is ridiculous that the stainless steel sewage pumps provided by the agents of one manufacturer in different places are totally different.   The is the primary stage of fake pump making.

4.The middle stage of fake stainless steel sewage pump making

In some cases, the agent sells many stainless steel sewage pumps produced by illegal enterprises. In order to cover the truth, they will let the illegal enterprise make a model for the logo of official manufacturer.

5.The advanced stage of fake stainless steel sewage pump making

The agent and the manufacturer will cooperate to make fake stainless steel sewage pumps, along with many fake certificates and honors.

Specific speed of stainless steel submersible pump

We can use a formula to calculate the specific speed of stainless steel submersible pump.

Stainless steel submersible pumps are different in impeller structures, hydraulic performance and size. In order to divide them into groups and put the similar models into one group, we need a comprehensive parameter. The parameter shall reflect the common features of water pumps.

This comprehensive parameter is specific speed of the stainless steel submersible pump, signified by ns.

1.The definition of specific speed

Scale down the size of stainless steel submersible pump at its highest efficiency or scale it up until the effective power reaches 0.7355 kw, head 1 m, flow quantity 0.075 m3/s. By then, the rotation speed of this model pump is the specific speed of the real pump it comes from.

2.Calculation formula of specific speed

ns=3.65n multiplied by the square root of Q and then divided by H. You can get it through the principle of similarity.

3.Matters need attention when using this calculation formula

Q and H refer to the flow quantity and head of the stainless steel submersible pump when it is at its highest frequency. N refers to the designed rotation speed of the pump.

The specific speed of each stainless steel submersible pump is certain.

In case of single stage double suction centrifugal pump, we calculate with half of the flow quantity. In case of horizontal multistage pump or vertical multistage stainless steel submersible pump, we should calculate with the flow quantity of one stage of impeller.

We calculate the specific speed on the base of the stainless steel submersible pump delivering clear water at 20 centigrade degrees.

The unit of each parameter should be same as the model pump.

4.Discussion about the specific speed

Specific speed is not the actual rotation speed of the stainless steel submersible pump. It is just a uniform standard for the performance of each kind of pump.

Therefore, its unit is not meaningful, often omitted.

Although the specific speed of the stainless steel submersible pump is calculated through the principle of similarity, but it also contains the main parameters of the actual pump, like Q, H and n.

Hence, it reflects the main performance of the stainless steel pump.

For more information, please contact info@welpump.com.