HYDRAULIC POWER UNITS Stone Power Units are a high quality small power unit that has the flexibility in design to be applied to a large range of applications. Kept in store at PT Hydraulics as "Standard Packs" or can be ordered with many different options to suit your application. PT Hydraulics build custom packs in Melbourne for a diverse range of OEM's here in Australasia. Our test facility and the Engineering support of SPX in the USA gives PT the ability to support the Stone range from production to service and warranty.