3.2 M a t e r i a l . - All materials shall be suitable for the purpose intended
and shall be in accordance with or equal to the applicable specification specified
in section 2. Nodular iron and "mechanite" castings in accordance with Speci-
fications MIL-I-17166 and QQ-I-652 respectively shall be considered for pump
and motor cases, end caps, covers, bases, and similar items. Castings shall
be clean, homogeneous and entirely suitable for oil hydraulic power transmission
service. Impregnation of nonferrous castings for the purpose of sealing minor
porosity will be given consideration upon application to the bureau or agency con-
cerned for permission to use the process. The impregnation process, where used
shall be in accordance with Specification MIL-I-17414.
3.3 General design.-
Pumps and motors shall be furnished in sizes as specified
3.3.1 S i z e s . -
(see 6 . 1 ) .
3.3.2 Pumps and motors shall be suitable for either standard or heavy
duty service. Standard duty shall render a minim urn varying service of
5000 hours Heavy duty shall render a minim urn varying service of 10,000 hours
(see 6. 1).
3.3.3 Ruggedness.- Pumps and motors shall be of substantial construction,
Design shall be in accordance with best m odern engineering practice, There
shall be no excessive vibration of moving parts under any conditions of operation
up to and including 115 percent of rated speed. Pumps and motors shall operate
without loss in performance at any position from normal up to 30 degrees either
side of normal, such positions being due to roll of the ship on which the equip-
ment is installed.
3.3.4 Factor of safety.- Stresses under normal full-load condition shall
not exceed 35 percent of the minimum urn yield point of the material used and, under
extreme loading (for example, impact loading) the combined stresses shall not
exceed 70 percent of the minim urn tensile yield point (t.y.p.) of the material used.
The following yield points may be assumed:
(a) Direct shear -60 percent t.y.p.
(b) Torsional shear -60 percent t.y.p.
(c) Static bearing -160 percent t.y.p.
3.3.5 Mounting. -
3 . 3 . 5 . 1 Pumps.- Pumps shall. be designed to be base or flange mounted
as specified (see 6 . 1 ) .