If water is supplied to pipes at low pressure, or not at all, there are many possible causes. Sometimes the pressure of the municipal water supply is not sufficient to meet the needs of the building in question, making a pressurization system necessary. However, there are also cases where internal plumbing problems make water distribution difficult, even if the supply pressure is adequate.
When a tall building has water pressure problems, the first step is to identify the causes, as installing the wrong solution is a waste of money. For example, installing a booster pump when low pressure is due to clogged pipes causes unnecessary energy expenditure and can even cause pipes to burst.
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Scenario #1: Adequate water supply pressure and plumbing system problems
If the municipal water supply has adequate pressure, but there are still plumbing fixtures with insufficient flow and pressure in the building, there are several possibilities. Clogged pipes are often found in older installations where the build-up of rust and sediment over time causes a drastic reduction in the internal diameter of the piping, occasionally blocking the pipes completely. Sometimes the damage is also evident on the surface, but a pipe can also appear to be in working order while it is clogged internally. Sometimes piping can be cleaned and restored, but it may need replacement if the damage is extensive.
Low water pressure can also occur in newer installations if piping is specified too small due to errors during plumbing design. Clogged pipes and undersized pipes have the same effect – flow restriction and pressure drop.
Faulty valves can also cause water pressure problems, as can valves that have been left partially closed by accident. The best way to identify and locate problems with your plumbing system is to have a professional building inspection.
Scenario #2: Low pressure in the water supply
If the municipal water supply does not have sufficient pressure at the service inlet, effective water supply to upper floors may be impossible, even with a completely new plumbing installation. There are also cases where the building is simply too tall for the municipal water supply to reach the upper floors without reinforcing the equipment. The three main types of pressure boosting systems approved by the New York Building Code are as follows:
- Elevated water tank
- Hydropneumatic pressure amplifier
- Water Pressure Booster Pump
Elevated water tanks simply take advantage of gravity to deliver water to pipes at proper pressure and flow rate. A pumping system refills the tank when the water level drops below a certain level and shuts off when the tank is full to prevent overflows. The pump ensures water availability, while the elevated tank provides the necessary pressure. The advantage of this configuration is that the pumping power is reduced, compared to a system where pressure and flow must be established with a water pump.
The New York Plumbing Code establishes a series of requirements to prevent contaminants or vermin from entering these tanks. Most of these tanks are made of wood or steel in New York, but other materials with equivalent mechanical properties are permitted. For a given storage capacity, a firewood tank is less expensive but more demanding in terms of maintenance.
Hydropneumatic pressure amplifiers use an airtight tank filled with water, pressurizing the air inside until it reaches a specified value, at which point the pump is turned off. Because the water is pushed downward by the tank's pressurized air, it can be delivered to the pipes at adequate pressure even when the pump is off. As the water level in the hydropneumatic tank decreases, the pressure is reduced and the pump is activated again when the lower limit value is reached. For this type of pressure boosting system, the New York Plumbing Code requires the installation of a pressure relief valve, selected and set according to the tank's maximum pressure rating.
Elevated water tanks and hydropneumatic pressure boosters rely on a pump that is turned on and off as needed, but they differ in how the pump is controlled.
- The pump that supplies water to an elevated water tank is activated at the lower level and deactivated at the upper level. It does not work immediately when the water level starts to drop, to avoid short cycles.
- On the other hand, pumps that supply water to hydropneumatic pressure boosting systems are turned off when the system pressure drops below a specified value and restart when a higher pressure is established. As with elevated tank systems, the pump is not restarted immediately when the pressure begins to drop, to avoid short cycling.
The water pressure booster pump operates directly on the water supply line to increase pressure. A very important design consideration is that pressure is reduced at the pump suction, therefore a cut-off switch must be installed to prevent cavitation, which can cause serious damage to the pump impeller and other system components. New York plumbing code requires the cutoff switch to be activated whenever the pump inlet pressure drops below 10 psi.
Keep in mind that deficiencies in the plumbing system and low pressure in the water supply can be present simultaneously in a building, and the best way to determine this is through a professional assessment.
Importance of engineering design in pressure boosting systems
Design services not only ensure pressure boosting systems meet New York codes. They also prevent excessive pressure and flow, which have two negative consequences:
- They represent a waste of pumping energy.
- Excessive flow increases the energy consumption of domestic hot water systems as there is more water circulating through them.
Rules of thumb can be a tempting approach when sizing mechanical and plumbing equipment because of their simplicity. However, they typically result in oversized installations that are inefficient and bring additional maintenance problems.
The New York Plumbing Code provides a table of the minimum flow rate and pressure that must be provided for each type of plumbing. When the pressure does not reach these values and the plumbing system is in good condition, a pressure increase system is necessary. In New York City, municipal water supply pressure is generally sufficient for buildings up to five stories tall. Above this point, a reinforcement system is normally required.
