The underground hydrant shown here was developed around 1849 and is of the "ball type". The hydrant standpipe itself was portable, attached to the hydrant only when needed, much the same as with today's underground hydrants. However, the mainvalve consisted of a ball held by water pressure against a seat in an iron chamber. Later models had valves which were spring loaded overcoming the problem of the valve not seating when the water pressure was low.