# Homework Help: Pressure washer

1. Jun 15, 2009

### Cret

I'm having trouble with this question. Any guidance would be very welcome. I have left the values out because i want to do the maths myself.

Data
Pressure washer delivers xxx litres per hour of water
Pressure xx bar
Draws xxxx Watts of power

Question
a.) Show power in water flow is xxx watts
b.) Calculate efficiency between electrical input energy to hydraulic energy in water
c.) Calculate diameter of output nozzle of the washer
d.) Use the cross sectional area of the nozzle to calculate the reaction force exerted on the user

Attempt thus far:

P = Power (Watts)
p = Pressure (N/mm2)
Q = Flow rate m3/s
n = Efficiency
v = velocity (m/s)
A = Area
Vjet = velocity of jet
g = 9.81

For a.) I used

P = p x Q
Converting xxx litres per hour to litres per second and xx bar to N/mm2

For b.) I used

n = output / input = answer x 100%

For c.)

Initially I found the velocity of the output jet in meters per second

Vjet = sq root 2 x g x p = m/s

Then I rearranged

Q = v x A
A = Q/v

Which gave me the cross sectional area of the nozzle

For d.) I’m have a little trouble with the final part

2. Jun 15, 2009

### RTW69

The reaction force is the force required to hold the power washer nozzle steady. Use Linear momentum, F= ma=mass flow rate X Velocity. You know Q in l/hr, the density of water and velocity of the water.

3. Jun 18, 2009

### Cret

Many thanks this helped at lot!