The two engines at Ryhope are identical, apart from one being a mirror image of the other. They are described as double-acting, compound rotative beam engines. ‘Compound’ means that the engine has more than one cylinder; high pressure steam from the boiler enters the high pressure cylinder then passes via any intermediate cylinders to the low pressure cylinder, so as to get as much energy from the steam as possible – there are two stages in the Ryhope engines. ‘Double-acting’ means that steam acts alternately on the top then the bottom of the piston – in other words steam pushes the piston down, then pushes it up.