To maintain a stable pressure in the water supply system, a hydraulic accumulator is installed. It is a sealed container, separated by an elastic membrane. Liquid accumulates in the tank, which is dispensed at the right time. What value of air pressure should be in accumulators is set by the manufacturer. When installing the system, you can calculate the optimal parameters and make adjustments yourself.
Pressure value in the accumulator
There are two media inside the hydraulic tank - air or gas and water, which fills the rubber membrane. The principle of operation of the device: when the pump is turned on, the liquid enters the expanding container. The gas is compressed, its pressure increases. The air pressure pushes water out of the membrane into the piping. Upon reaching the indicator for which the automation is configured, the device turns off. Water consumption comes from the accumulator stock. The decrease in the volume of the liquid leads to a drop in pressure and the re-starting of the pump. The operation of the hydraulic accumulator is monitored by a pressure switch.
The main function of the pressure in the accumulator is to create optimal conditions for the operation of the pumping station. The air pressure excludes the switching on and off of the mechanism after each opening of the tap. Installing the storage device in the water supply system also solves other problems:
- Prevention of abrupt changes in pressure in the pipeline (water hammer), causing damage to pipes and mixers.
- Extension of the service life of pumping equipment, prevention of wear of parts and assemblies.
- Creation of a supply of water inside the tank, which is used in case of a power outage.
The choice of tank volume depends on the power and type of pump. Units with a built-in frequency converter are characterized by smooth start-up. A tank with a minimum capacity (24 l) is sufficient for them. Lack of mechanisms, high cost, they are rarely used in private households. A common option is budget borehole pumps that give maximum power when started. They quickly create a high head in the pipes. The diaphragm tank should compensate for it.
When operating surface pumps with a power of up to 1 kW, it is recommended to install a 24-50 liter accumulator. For submersible units with a power of 1 kW, a hydraulic accumulator of 50-100 liters is required. Mechanisms with professional characteristics are completed with tanks from 100 liters. The size of the storage tank is influenced by the average water consumption.
Types of accumulators
Capacities differ in size, purpose, performance. The design and function of the tanks remain unchanged.
- for hot water (red);
- for cold water (blue).
The difference between the storage tanks is in the material from which the membrane is made. In a container intended for drinking (cold) water, rubber that is safe for human health is used.
- vertical models - used for limited space;
- the horizontal version is used in conjunction with an external pump fixed to the body.
Each type of device is equipped with a special air release device. A valve is installed in the upper part of the vertical hydraulic tanks. The accumulated air is released through it, preventing the formation of blockages in the system. In tanks of the horizontal type, a unit of pipes and ball valves is provided. The drain is carried out into the sewer. In tanks with a volume of less than 100 liters, valves and drain assemblies are not installed. Air is removed during preventive maintenance.
The drives are installed in heated rooms. The instruments must be freely accessible for repair and maintenance.
- The correctness of the choice of the maximum and minimum pressure at which the automatic pump activation is triggered.
- Competent setting of the air pressure level in the tank.
When performing self-checking and adjusting indicators, you should adhere to the recommendations of specialists. The basic rule is that the air pressure in the pumped storage tank must be below the minimum pressure for switching on the pump. The difference in indicators is 10-12%. Compliance with the recommendation allows you to save a small amount of water until the next start of the unit. Example: if the pumping station starts automatically at 2 bar, the air pressure should be 2-0.2 = 1.8 bar.
The air pressure in the storage tank is independent of its volume. The average for containers with a size of 24-150 liters is 1.5 bar, 200-500 liters - 2 bar. The initial factory air injection in 1.5 atmospheres in conditions of low water consumption of a one-story building can be reduced to 1 atmosphere. The low head in the pipes reduces wear on the system, but limits the use of plumbing fixtures. Decreasing the pressure to less than 1 bar will result in overstretching of the rubber bulb. The diaphragm will come into contact with the metal body. Contact will lead to accelerated wear of the rubber.
Excessive air pressure (more than 1.5 bar) is also not desirable. It will take up most of the tank, reducing the amount of water drawn. There will also be an increased load on pipes and components of the water supply system.
The water pressure in the membrane is generated by a pump. Its maximum allowable value is indicated by the manufacturer. A common indicator for household models is 10 bar. When connecting a hydraulic accumulator, fluid is fed into the system slowly to avoid damage to the diaphragm.
To calculate the optimal air pressure in the tank, there is a formula: P = (Hmax + 6) / 10, where
- P is the air pressure in atmospheres;
- Hmax is the distance to the highest point of the domestic water supply system.
The top parsing point is the shower on the top floor of the building. The distance from it to the place of installation of the pressure vessel is measured. The larger the gap, the higher the head required to lift the water. The use of numbers will add clarity to the calculation. For a building with a height of 2 floors, the value of Hmax will be 7 m. The pressure will be P = (7 + 6) / 10 = 1.3 atmospheres. For a height of 10 m, a head of 1.8 atmospheres is required.
Before buying a hydraulic accumulator, the volume of the device is calculated. Calculations take into account:
- maximum water consumption;
- number of pump starts per hour;
- air pressure in the tank;
- lower and upper pressure limits for pump operation;
- coefficient related to the pump power.
After installing the membrane tank, it will be necessary to set the minimum and maximum threshold for the automatic operation (pressure switch). The difference between the maximum and minimum indicator determines the volume of water coming from the hydraulic accumulator. Increasing the parameter increases the efficiency of the device, but leads to rapid wear of the membrane. For private houses a difference of 1-1.5 bar is recommended.
The indicator of the minimum pressure in the diaphragm (Pmin) must be 10% higher than that of the air in the tank cavity.For stable operation of the system, the differential pressure must be 0.5 bar or more. This value is taken into account when calculating Pmin. The upper limit of operation (Pmax) is calculated based on the characteristics of the pump - the head is divided by 10. The calculated value does not correspond to the real one due to changes in the declared parameters of the unit associated with wear. It is recommended to take the upper level indicator 30% less than the head characteristic.
The air pumped into the tank at the factory gradually leaves through the rubber membrane and nipple. Vacuuming the gas cavity causes the rubber bulb to overstretch when filled with liquid. Without resistance, the membrane wears out quickly and may burst. Air pressure measurements are performed with a pressure gauge. The best option is an automotive measuring device.
The manufacturer's instructions indicate the number of checks for the device model. Average rate - 2 times a year. Before starting the procedure for measuring the parameter, it is necessary to drain all the liquid from the tank. The pump is disconnected from the power supply system. At the time of measurement, the tank must be empty. Control is required before connecting the device to the system. Part of the air may escape from the tank during storage. The working pressure is indicated in the product data sheet.
To check, unscrew the decorative cap that covers the nipple. The node is located at the top of the body. A pressure gauge is connected to the spool. The device should have a minimum error. Electronic and automotive devices are recommended. It is better not to use cheap plastic pressure gauges, they have a significant error of indicators. If the level is less than the factory parameters, air is pumped up using a compressor. The accumulator is left for a day for monitoring. After the next measurement corresponding to the norm, the device is installed. Exceeding the optimum head is eliminated by bleeding air.
The number of checks depends on the length of time the plumbing system has been used. For summer cottages where communications are operated in the spring-summer period, indicators are monitored before the start of the season. A sign of a decrease in the air pressure is the frequent switching on and off of the pump. In case of any deviations from the norm, an unscheduled check is carried out. A slight loss of air can be pumped up with an automobile pump.
How to properly adjust the pressure in the accumulator
Correct operation of the pumping station requires competent adjustment of three main parameters:
- The pressure at which the pump is turned on.
- Shutdown level of a running unit.
- Air pressure in the membrane tank.
The first two parameters are controlled by the pressure switch. The device is installed on the inlet connection of the accumulator. Its adjustment takes place empirically; to reduce the error, actions are performed several times. The relay consists of two vertical springs. They are seated on a metal axle and secured with nuts. Parts differ in size: a large spring regulates the activation of the pump, a small one is required to set the difference between the upper and lower pressure. The springs are connected to a membrane making and breaking electrical contacts.
Adjustment is done by turning the nut with a wrench. Clockwise rotation compresses the spring and increases the pump activation threshold. Counterclockwise rotation weakens the part and decreases the trigger parameter. The adjustment procedure takes place according to a certain scheme:
- The air pressure in the tank is checked, if necessary, it is pumped up by the compressor.
- The nut of the large spring turns in the desired direction.
- The water discharge valve opens. The pressure drops, at a certain moment the pump turns on. The pressure value is indicated on the pressure gauge. The procedure is repeated if necessary.
- The difference in performance and the shutdown limit is adjusted by a small spring.It is sensitive to tuning, so it can be rotated half or quarter turn.
- The indicator is determined with the taps closed and the pump turned on. The pressure gauge will display a value at which the contacts open and the unit shuts down. If it is from 3 atmospheres or more, the spring should be loosened.
- Drain the water and restart the unit. The procedure is repeated until the required parameters are obtained.
The factory settings of the relay are taken as a basis. They are indicated in the passport of the device. The average pump start-up rate is 1.4-1.8 bar, shutdown rates are 2.5-3 bar.
Installation of a hydraulic accumulator in the water supply system allows you to maintain the pressure in an autonomous network and avoid water hammer. A functioning accumulator reduces the number of starts and stops of the pump, preventing wear on the mechanism. Timely checks and adjustments of the air pressure in the tank will ensure the operating condition of the system for several years.