# Residual pressure in a fire sprinkler system

• TSN79
In summary, the conversation discusses the relationship between pressure drop and flow in a piping system, particularly in regards to sprinkler valves and residual pressure. The principle is that more flow results in a larger pressure drop, and in order to achieve the desired flow rate, the pressure at the sprinkler valve must not fall below a certain level. It is important for the designer to ensure that the supply can deliver the necessary pressure at the required flow rate, taking into account the pressure loss in the pipework.
TSN79
I'm aware that the term means the remaining pressure at a point while there is flow. Say the distribution pipes downstream the sprinkler valve have a calculated total head loss of 3 bars during the designed flow. Does that mean that the residual pressure at the sprinkler valve needs to be at least 3 bars to achieve the designed flow? It just seems so unintuitive to me. After all, if I get the designed flow at a lower residual pressure, why would that be an issue?

I'm not 100% sure where the sprinkler valve is in your system, or where you measure residual pressure. But your questions all seem to relate to the relationship between pressure drop and flow.

Consider the following simple piping system. Water flows in the direction of the arrow. The box represents any collection of pipes, elbows, open or partially open valves that you like. The pressure difference Pa-Pb is the pressure loss across the whole collection.

Now the basic principle is that the more flow we have, the larger Pa-Pb becomes. Usually is is proportional to the square root of Pa-Pb, but that doesn't matter. What does matter is more flow means more pressure loss. It does not matter which words you use to label Pa and Pb, nor does it matter how big Pa is or Pb is. Only the difference Pa-Pb matters. You can not get more flow without increasing Pa-Pb.

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The sprinkler valve represents the beginning of the system, and is also where the residual pressure is measured. Let's say point Pa represents this location. Once there is flow, the pressure reading at Pa will start to fall. Is there a need for Pa not to fall below 3 bars (if the calculated loss is correct) in order to achieve the desired flow rate? Appreciate the help :)

Each sprinkler head will deliver the specified flow at a specified pressure. You or the designer has to ensure that pressure is maintained under worst case conditions or the flow will be lower.

If you provide 3 bar at the inlet valve and the loss in the pipework is 3 bar then the pressure at the sprinkler will be low so the flow might be inadequate.

I think you need to find out what pressure is needed at the sprinkler heads and add the 3bar pipe loss to that.

The supply must be able to deliver that pressure at the required flow rate (eg not just the static pressure).

## 1. What is residual pressure in a fire sprinkler system?

Residual pressure in a fire sprinkler system refers to the pressure that remains in the system when all the sprinkler heads are closed. It is the minimum pressure required to activate the sprinkler heads in case of a fire.

## 2. How is residual pressure measured in a fire sprinkler system?

Residual pressure is measured using a pressure gauge, which is typically installed at the main water supply to the sprinkler system. The gauge displays the pressure in pounds per square inch (PSI) and can be read manually or electronically.

## 3. What factors can affect the residual pressure in a fire sprinkler system?

The residual pressure in a fire sprinkler system can be affected by several factors, including the elevation of the building, the size and length of the water pipes, the type of sprinkler heads, and the water supply pressure from the main source.

## 4. Why is residual pressure important in a fire sprinkler system?

Residual pressure is important because it ensures that the sprinkler heads have enough pressure to activate and spray water in case of a fire. Without sufficient residual pressure, the sprinkler system may not be able to effectively control or extinguish a fire.

## 5. How can the residual pressure be maintained in a fire sprinkler system?

The residual pressure in a fire sprinkler system can be maintained by regularly checking and testing the system to ensure that all components are functioning properly. Any leaks or blockages should be promptly addressed, and the system should be periodically flushed to remove any debris or sediment that can affect the pressure.

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