Unit 305 Session 6 Flow, force and pressure

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Plumbers Cymoedd

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24 Slides • 17 Questions

Pressure, force and flow of water

The SI units of Flow, force and pressure

However, in plumbing systems, flow rate is usually measured in litres per second (l/s) or (l/m)

Poll

Which of these do you think describes Flow rate?

Flow rate is the volume of fluid that passes through a given point or surface per unit of time, typically measured in litres per second (l/s) or litres per minute (l/m).

Flow rate is the pressure exerted by a fluid in a pipe or container, usually measured in Pascals (Pa).

Flow rate is the total mass of fluid that flows through a system, measured in kilograms (kg) per unit of time, regardless of the fluid's density.

In plumbing, flow rate is defined as an amount of fluid that flows through a pipe or tube over a given time.

It is usually measured in litres per minute (l/m)
or litres per second (l/s).

Plumbing systems in the UK must comply with specific building regulations and standards, such as the Water Supply (Water Fittings) Regulations 1999.

These regulations set maximum and minimum flow rates for different types of water fittings (e.g., taps, showers, toilets) to prevent waste and ensure water is used efficiently.

Force and Pressure

Open Ended

Describe what you think the difference is between force and pressure

Type response here

Force is an influence on an object at rest that, acting alone, will cause the motion of the object to change.

If the object at rest is subjected to a force, it will start to move. For example, consider water in a pipe connected to a cistern at one end and a tap at the other.

When the tap is closed, the water is not moving and so is said to be at rest.

When the tap is opened, the force of gravity will move the water out of the tap, causing water to flow.

The unit of force is the newton.

It is the force required to accelerate a mass of 1 kg at 1 metre per second, every second.

On Earth, that force of acceleration (known as gravitational pull) is 9.81 metres per second per second, or 9.81 m/s2.

Therefore, if we multiply the mass of an object (in kg) by 9.81, the result is measured in newtons.

Consider the cistern in the picture.

If it contained a mass of water equal to 40 kg, then by multiplying the mass by the force of gravity, the force of the cistern acting downwards can be calculated:

40 × 9.81 = 392.4 N

40kg

Force
⋁

392.4 newtons of force
acting on the tap

Static pressure of water (head)

The unit of pressure is the pascal.

The pressure exerted by water is due to its mass and is determined by the height of the column of water.

Pressure is defined as force per unit area.

For an object sitting on a surface, the force pressing on the surface is the weight of the object measured in newtons per square metre (N/m2).
However, in different orientations it might have a different area in contact with the surface and will therefore exert a different pressure.

They both exert the same force on the floor, however as cistern 1 has a smaller area on its base it will exert more pressure.

Pressure = Force
Area

Pressure is expressed in pascals
p