When the vacuum pump comes on, five pounds of force per square foot push down on the fabric.
( ( When ( ( the ( vacuum pump ) ) ( comes on ) ) ) ( , ( ( ( five pounds ) ( of ( force ( per ( square foot ) ) ) ) ) ( ( ( push down ) ( on ( the fabric ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NN vacuum) (NN pump)) (VP (VBZ comes) (PRT (RP on))))) (, ,) (NP (NP (CD five) (NNS pounds)) (PP (IN of) (NP (NP (NN force)) (PP (IN per) (NP (JJ square) (NN foot)))))) (VP (VB push) (PRT (RP down)) (PP (IN on) (NP (DT the) (NN fabric)))) (. .)))
When the pump starts up, the force is on the fabric to prepare it to be sewn.
( ( When ( ( the pump ) ( starts up ) ) ) ( , ( ( the force ) ( ( is ( on ( the ( fabric ( to ( prepare ( it ( to ( be sewn ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NN pump)) (VP (VBZ starts) (PRT (RP up))))) (, ,) (NP (DT the) (NN force)) (VP (VBZ is) (PP (IN on) (NP (DT the) (NN fabric) (S (VP (TO to) (VP (VB prepare) (S (NP (PRP it)) (VP (TO to) (VP (VB be) (VP (VBN sewn))))))))))) (. .)))