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24-hour wettest in constant operation against shutoff head.Conventional centrifugal sewage pumps are usually less <br /> satisfactory for STEP system service because of their flat characteristic curve,but may be considered case-by-case <br /> for extremely low-head installations.Grinder pumps are unacceptable for discharge to STEP systems because of <br /> solids and grease. <br /> IN Pressurized service lines from a STEP tank to the common collector sewer shall be minimum I"diameter.A <br /> shutoff valve(gate,plug,or ball)shall be installed in a tamperproof valve vault at property line.Unless otherwise <br /> approved,a swing check valve shall be installed in the same vault,and an additional swing check valve shall be <br /> installed at the tank outlet.Valves shall be full-port type and constructed of non-corrodible materials such as plastic <br /> and stainless steel. <br /> ■Gravity-flow service lines from STEG tanks to small-diameter gravity sewers shall be minimum 2"diameter.All '.. <br /> service lines shall have a minimum capacity of 10 gpm flowing half full,based on Manning's n=0.013.Each <br /> service line shall be vented at the upper end.Venting shall be continuous through the tank and building stack. <br /> PUMP CONTROLS <br /> ■Power is normally furnished by the USER.Pump control panels should be energized through a dedicated breaker <br /> in the building served. <br /> ■Control panels shall be NEMA.-4X with a locked door.Panels shall be exterior mounted and should be visible to <br /> OWNER's service personnel from public right of way.Electrical conduits shall be sealed gas-tight at the tank and <br /> the panel. <br /> ■Installations shall contain a high-water alarm switch,activating a user-cancellable buzzer and an alarm light. '.... <br /> Access to the light reset button shall be restricted to OWNER's service personnel.Alarms shall separately fused so <br /> that trip of pump breaker shall not disable an alarm. <br /> ■Pump control panels shall be equipped with elapsed time meters,and may also be equipped with event counters at <br /> the option of the OWNER.Operational controls shall be HAND/OFF/AUTO.Dual pumping units shall have <br /> operator-cancellable automatic alternators and event counters. <br /> COMMON PRESSURE SEWERS <br /> ■Common pressure sewers shall be minimum 2"diameter PVC or polyethylene pressure pipe,installed with toning <br /> wire or detectable tracer tape. <br /> ■Pipe sizing and layout shall generally conform with recommended practices in WFCP Manual of Practice FD-12, <br /> Alternative Sewer Systems,Table 2.1 and Chapter 3. <br /> ■Isolation valves,flushing connections,vacuum release valves,air release valves,and pig launching stations are <br /> optional.Such appurtenances shall be at the discretion of the engineer and the OWNER,subject to OAR 340-52 <br /> approval. <br /> COMMON SMALL-DIAMETER GRAVITY SEWERS <br /> ■Sewers shall be minimum 4"diameter,installed with tracer tape or toning wire. <br /> ■Sewers shall be designed to flow half full,based on 1 gpm per dwelling and Manning's n=0,013.Minimal <br /> velocities are acceptable.However,low-velocity and flooded sections may require sulfide controls. <br /> ■Subject to a 4"minimum diameter,inverted siphons shall be,designed to flow at a velocity of 0.5 feet per second <br /> or greater,based on a Hazen-Williams coefficient of 100. <br /> C <br />