TECHNICAL BROCHURE FHD-205

Basic two-pipe system with condensate pump

Bell & Gossett • Domestic Pump • Hoffman Specialty

Equipment & Definitionsin other two-pipe systemsDown-Feed Steam System – Heatingsystem in which supply main is abovelevel of heating units it serves.

Down-Feed Supply Riser – Verticalpiping that carries steam from overheadsupply main to heating units below.Supply riser must be dripped throughtrap to return piping.

Up-Feed Steam System – Heatingsystem in which supply main is belowlevel of the heating units it serves. Lowpoints of supply main must be properlydripped through trap to return piping.

Up-Feed Supply Riser – Vertical pipingthat carries steam from the supply mainup to the heating units.

Pressure Drop – Loss of pressure dueto pipe friction and the condensingprocess of steam.

Differential Pressure – Difference inpressure measured between inlet andoutlet of trap or similar equipment.

Mechanical Return System – Systemthat uses mechanical means (condensatepump) to return condensed steam (water)to the boiler. Pump must be located sothat condensate flows into receiver bygravity.

Vacuum Pump Equalizer – Pipingarrangement that equalizes inducedvacuum between the supply header andvacuum pump receiver.

Two-Pipe Vacuum System – Anordinary two-pipe vacuum system uses avacuum pump to create a subatmosphericpressure, usually 3" to 8" Hg. (Mercury),in the return piping. Vacuum removes airfrom system piping and heating units toprovide quick heating pickup and efficientsteam distribution. Condensate shouldflow to pump receiver by gravity.

Two-Pipe, Up-Feed System withCondensate Pump

Two-Pipe, Down-Feed System with Condensate Pump

Branching from main

Reducing size of main

Connections for upfeed risers

Upfeed branch frommain at 45° angle

Pipe expansionjoint for riser

Drop riser branched frommain top at 45° angle

Drop riser branchedfrom main bottom

Riser branched frommain bottom and

dripped into wet return

Double radiatorbranch from riser

Piping Ti p s

Two-Pipe Steam

Accumulator Tank – Where returnsin a vacuum pump heating system arebelow inlet connection of vacuum pumpreceiver, an accumulator tank needs tobe installed. Its location should be suchthat condensate flows by gravity to theaccumulator, and is lifted to vacuumpump receiver.

Flash Steam – Re-evaporation ofcondensate back into steam. It occurswhen condensate flows into a reducedpressure area where the condensate’stemperature is above boiling point forthe reduced pressure. For example: If hotcondensate is discharged by a trap intoa low pressure return or into atmosphere,a certain percentage of water will beimmediately transformed into steam.Flash steam usually has a white, puffyappearance.

Cooling Leg – Alength of uninsulatedpipe with sufficient cooling surface todissipate enough heat so that steamcondenses and trap can open to dischargecondensate from unit. Needed only withthermostatic traps.

Water Hammer – Water hammer isone of the chief causes of noise in steamheating systems a nd also the majorcause of damage to thermostats and floatsin traps. It is a wave transmitted through apipe filled, or partially filled, with water.It may originate as waves set up by steampassing at a high velocity over condensatecollected in piping.

Fig. 3-19 illustrates how such a wavemay be formed. The rapid passage ofsteam over the surface of the watercauses a wave to form as at “B”. Therapid condensation of the steam inpockets “A” brings the two slugs of watertogether with a considerable force, whichmay be telegraphed through the piping.

Heating SystemsTypical Two-Pipe Vacuum System

Two-Pipe Vacuum System withAccumulator Tank

Looping steam mainaround an obstruction

Looping dry returnaround door(two-pipe system)

Offset pipe calculation table

Drop riser or end of maindripping into dry return

(two-pipe system)

Supply main end dripping into dry return(two-pipe system)

Boiler piping to main Lift Fitting Detail

Fig. 3-19

Xylem Inc. 8200 N. Austin Avenue Morton Grove, Illinois 60053 Phone: (847) 966-3700 Fax: (847) 965-8379www.bellgossett.com

Bell & Gossett is a trademark of Xylem Inc. or one of its subsidiaries. © 2013 Xylem Inc. FHD-205 November 1997

There’s one pre-eminent name among two-pipesteam-heating-specialty manufacturers : Hoffman Specialty