254 also defines an outer diameter 270 which is smaller than an outer diameter 272 of the forward portion 256 referring to fig3 the secondary piston assembly 108 is depicted the secondary piston assembly 108 includes a body portion 300 a forward portion 302 a rear member 304 and a front member 306 while the rear member 304 the body portion 300 and the forward member 306 are depicted as three separate members the reader should appreciate that these members may be integrally formed as a single component the rear and forward members 304 and 306 include shoulders 305 and 307 respectively for receiving ends of the springs 112 and 113 shown in phantom therefore a biasing force generated by the spring 112 may be exerted on the shoulder 305 of the rear member 304 which is configured to transfer the biasing force to the body portion 300 and to the forward member 306 similarly a biasing force generated by the spring 113 may be exerted on the shoulder 307 of the front member 306 which is configured to transfer the biasing force to the body portion 300 and to the rear member 304 the rear and front members 304 and 306 include cavities 308 and 310 for receiving head portions 362 of shafts 360 of the poppet valve assemblies 106 and 110 respectively as described in further detail below with reference to fig4 the rear member 304 terminates in a washer 312 which defines an opening 314 the inner diameter of the opening 314 is larger than the outer diameter of the shaft 360 and smaller than the diameter of the head portion.