The Big Idea

Just been checking the solar water heating system and noticed the pressure was low. It's been 2 years since the last maintenance, so I plan to convert this old shower pump into an air purge and charging pump for the maintenance of the solar circuit.
Saves paying out to plumbers, who usually don't understand the system anyway. Last time they came back twice and still ballsed it up, so I eventually had to get in a guy from the supplier.
Now I'll do it myself and save a fortune!