In some cases unsupported lengths of stem are subjected to buckling under compression or from lateral thrust by debris or solids. Stem guides are therefore, necessary as a means of providing intermediate support.
Bolt on type adjustable guides are manufactured in mild steel normally plain or stainless steel unmachined, but if required they can be bronze lined. When considering the centres of vertical spacing of the guides, the l/r (length/radius of gyration) should not normally exceed 200.
There are several methods of connecting sections of stem together. The type selected will depend upon the application and the duty of the penstock. The most commonly used couplings are illustrated below.
Manufactured in cast iron, for joining straight lengths of stem in line. For use with torsional loads only (non-rising stem applications)
Manufactured in the same material as the stem for joining straight lengths of stem in line. For use with both axial and torsional loads (rising and non-rising stem applications).
Two types of coupling are available:-
Plain muff coupling
Screwed muff coupling
The use of particular type of coupling will depend on the operating duty and/or the specification
Manufactured in mild steel or stainless steel, for joining two straight lengths of stem in different planes. For transmission of torsional loads only (non-rising stem applications). Universal joints are supplied in pairs for a maximum working angle of 450.