Search for hydraulic ram pump or just ram pump for lots of great home made pumps and vids on their operation e.g. https://youtube.com/results?search_query=ram+p

Search for hydraulic ram pump or just ram pump for lots of great home made pumps and vids on their operation e.g. https://youtube.com/results?search_query=ram+pump https://youtube.com/results?search_query=ram+pump