Hydraulic pole tampers are for compressing/tamping the soil/earth around poles, either in installation or maintenance of poles. They are also used by utilities and contractors for power or lighting poles, fencing, support poles for shading (playgounds, tree orchards), and more. They are a specialised jack hammer, have a rounded kidney shaped foot with several options in size and operation (switch on tube end, inline hose switch). These hydraulic rammers require a low pressure power source and are often powered from an EWP truck (elevated work platform or aerial bucket) but can also be powered from a pump (petrol/electric/diesel) or other hydraulic machinery (bobcat, forklift, tractor, etc - sometimes they require a flow control valve depending on machinery pressure and flow rate). Hydraulic tampers are used with hydraulic hose sets. Benefits of hydraulic tampers can include long periods of usage, can also be more powerful and weigh less than on board petrol units.
Alternate terminology: Hydraulic Post/Pole Hole Tamper, Hydraulic Backfill Tamper, Hydraulic Pole Rammer.