One of the most frequent phone calls we receive is from contractors and engineers asking “Is a Hammer delivering full energy if the blow count per minute is less than listed in the Specifications?” Blow count does not indicate full or less than full energy.
A Single Acting Hammer will deliver full energy if the stroke is as listed in the Specifications. The length of the stroke is the only criteria of a Single Acting Hammer delivering full energy.
A Super Vulcan Differential Hammer derives some of its energy on the down stroke from the air or steam pressure. A Super Vulcan Hammer in proper condition will deliver full energy if the P.S.I. at the Hammer is as listed in the Specifications. The striking energy of a Differential Hammer will vary directly with the steam or air pressure (see Vulcan Tip Issue No. 4 ).
The blow count (not the energy) of any Hammer will be effected by the amount of Pile set on each blow, type of cushion material, the amount of cushion material. Too little cushion material will cause the Hammer to over stroke.
In Specifications published before 1972, blow count was listed as “blows per minute at normal stroke and no set”. This means, if the P.S.I. at the Hammer is as listed in the Specifications, the Hammer is functioning properly and the Pile is at refusal.
Note: this topic–a recurring theme for Vulcan hammers–is dealt with again in Vulcan Tip 68.