How to choose a sand tank?

I. Selection of swimming pool sand tank

Often, customers inquire about the size of the sand tank that should be used for their swimming pool. Generally, the size and quantity of the sand tank selected for the swimming pool are determined by the size of the swimming pool and the circulation time. The specific calculation method is as follows:

Pool water volume V = Length X Width X Average depth

Circulation flow rate Q = Pool water volume X 1.05 ÷ Circulation period 4 hours

Note: The circulation period of the swimming pool is 4 hours.

For example: A swimming pool is 25m long, 16m wide, and has an average depth of 1.4m. Then the pool water volume is 25m X 16m X 1.4m = 560m³. With a 4-hour filtration cycle, the circulation flow rate is 560m³ X 1.05 ÷ 4 hours = 147m³/h.

The swimming pool circulation flow rate is 147m³/h. Then, based on a medium-speed filtration (25m/h), according to actual needs, four sand tanks with a diameter of 1400 can be selected for filtration (unit: millimeters). (↑ Olyris top-out swimming pool filtration sand tank)

Note: The filtration speed is the amount of water filtered per unit area in a unit time. To standardize the filtration speed of the filter and facilitate selection, the filtration speed v ≤ 10m/h is called low-speed filtration; the filtration speed is 11-30m/h, it is called medium-speed filtration; the filtration speed is 31-50m/h, it is called high-speed filtration.

Practice has proved that when the filtration speed is within the range of 10-25m/h, the filtration effect and pressure loss of the filter are proportional to the filtration speed. If the filtration speed exceeds 25m/h, the filtration efficiency decreases rapidly, that is, as the filtration speed increases, the water quality of the filtered water will deteriorate continuously. Therefore, to ensure that the water quality after filtration meets the requirements of hygiene, health, and clarity, the filtration speed of public swimming pools should be ≤ 25m/h.

II. Sand tank head and multi-function valves

For a long time, the Chinese translation or usage methods of sand tank heads and six-way valves have also been one of the popular consultation questions. How to install the specific interfaces on the sand tank head? There is a simple and understandable slogan: Upward inlet, downward outlet, side drainage. The meaning is very straightforward. Diagram: (↑ Sand tank head interface function diagram)

The functions and operation methods of the six positions of the sand tank multi-way valve:

1. FILTER normal filtration:

Press down and push the handle on the cylinder head controller to the (FILTER) normal filtration position, then start the water pump and perform a normal circulation filtration.

2. BACKWASH reverse flushing:

The sand in the sand tank forms millions of water passages, and various impurities are filtered and retained in the filter as the amount of impurities increases, and the water passage gradually decreases. This is why the pressure reaches 30 kPa (kpa) or more. Under this pressure, the sand tank cannot perform any filtration function, and it is necessary to clean according to the following steps: Close the water pump, open the multi-way valve to the "reverse flushing" position, open the bottom discharge and return circuit valves. Start the water pump for 3 minutes. When the operation is completed, the lumps of impurities will be removed.

3. RECIRCULATE external circulation:

This position, the multi-way valve controls the water flow from the water pump directly to the swimming pool water without passing through the internal filter.

4. WASTE discharge:

If the swimming pool water needs to be emptied, the multi-way valve can be placed in the WAST discharge position. When the motor is running, the drainage valve should be fully opened to ensure that the water pump has sufficient suction.

5. RINSE rinsing

After the sand tank undergoes BACKWASH reverse flushing, if the multi-way valve is placed back to the FILTER normal filtration position, the water flow will be a few seconds turbid. To prevent turbid water from entering the pool, the multi-way valve should be placed in the RINSE rinsing position.

6. CLOSED closing

This position is used to shut off the water flow from the filter to the pump, and is used when the hair collector of the pump is turned on.

(↑ Diagrams of two common modes of sand tanks used in swimming pools)

Precautions for using the sand tank of the swimming pool:

1. When turning the handle of the cylinder head control valve, the control valve handle must be pressed down to prevent damage to the valve seal!

2. When turning the control valve, the pump must be turned off!

3. Avoid allowing the sand filter tank to work under a pressure higher than 35 kilopascals (kpa)!

4. Regularly clean the hair collector!

5. Prevent leakage, confirm that all pipe connections are firm and reliable!

III. How often should the backwashing be performed?

There is no fixed pattern for the backwashing cycle of the sand tank. Just like eating, you can eat when you are hungry. Moreover, the application of the sand filter tank is very wide, used in different industries, and the amount of impurities varies, so the backwashing cycle also varies. Let's analyze the several factors that affect the backwashing cycle:

1. Different application places. For example, some customers use the sand filter tank to filter impurities in mountain spring water. In this case, the mountain spring water is generally clear, so it is possible to backwash once every ten days or half a month. But some customers use it to filter impurities in urban sewage. In this case, it may need to backwash once a day.

2. Different types of sand tanks. The flow rate of the sand filter tank will vary depending on factors such as the pump flow rate, sand layer thickness, sand material size, and filtration area. Under the same suspended matter content and the same flow rate, theoretically, the larger the sand tank, the larger the filtration area, the smaller the resistance of the water flow, and the higher the filtration accuracy. The backwashing cycle will also be shorter.

3. Different subjective judgments of the customers. Because some customers have subjective differences in the judgment of the sewage after backwashing. So the backwashing cycle also varies according to their judgment.

Solution: Based on the turbidity of the discharged water and the reading of the pressure gauge during the previous backwash, determine a cycle. For example, during normal filtration, the pressure gauge's count is 0.1 MPa. When the reading of the pressure gauge reaches 0.2 MPa, we perform a backwash once. We find that the discharged water is not so dirty. Then we understand that the next backwashing time can be extended. Repeat several times, and we record this time interval each time. We will obtain the best backwashing cycle.

(↑ Y series side-out swimming pool filter sand tank of Olis)

IV. When should the sand in the swimming pool sand tank be replaced?

The quartz sand of the swimming pool sand tank should be replaced once or twice a year. The reasons are as follows:

1. During backwashing, the filter layer will expand by 1.2 to 1.3 times its volume. The upward water flow will drive the filter layer to flow up and down, causing the filter material particles to collide with each other. Since the materials are the same, the hardness is the same, and therefore, some of the filter material will break into fine particles and be lost with the backwashing water;

2. Some quartz sand may have fusion phenomena due to insufficient purity when exposed to acid or alkali;

3. After long-term use, the internal part of the filter layer may be surrounded by gelatin due to uneven water distribution, losing its function;

Therefore, the longer the time, the worse the filtration effect of the sand tank. Since backwashing will consume and remove some sand, we need to replace the sand in the sand tank within the specified period.