Tube-pulling apparatus

Claim 1

Tube-pulling apparatus, comprising a cylinder, having a front end and a rear end; a stationary feed pipe extending into said cylinder from said rear end thereof, said feed pipe including supplying means for supplying fluid to said cylinder; a first piston slideably mounted on said feed pipe for reciprocating movement in said cylinder, said first piston including an interior cavity; a second piston mounted for reciprocating movement within said cavity of said first piston, said second piston cooperating with said first piston to form a chamber therebetween; expandable gripping means for releasably gripping an inner wall of a tube to be pulled from a tube sheet when said gripping means is expanded, said gripping means being fixedly connected to said second piston, whereby said gripping means is moveable conjointly with said second piston; expanding means for expanding said gripping means, said expanding means being fixedly connected to said first piston, whereby said expanding means is moveable conjointly with said first piston; first providing means for providing fluid communication between said feed pipe and said chamber, whereby fluid supplied to said chamber move said first piston towards said rear end of said cylinder while urging said second piston towards said front end of said cylinder; second providing means for providing fluid communication between said chamber and a front portion of said cylinder after said first piston has moved rearward a predetermined distance relative to said second piston, whereby fluid supplied to said front portion of said cylinder from said chamber causes the conjoint rearward movement of said first and second pistons, said second providing means including first inhibiting means for inhibiting fluid to flow from said chamber to said front portion of said cylinder until said first piston has moved rearward said predetermined distance; third providing means for providing fluid communication between said front portion of said cylinder and said chamber during the forward movement of said first piston in said cylinder, whereby fluid in said front portion of said cylinder is exhausted therefrom through said third providing means during the forward movement of said first piston in said cylinder, said third providing means including second inhibiting means for inhibiting fluid to flow from said chamber to said front portion of said cylinder at least until said first piston has moved rearward said predetermined distance, said second inhibiting means cooperating with said first inhibiting means to prevent any rearward movement of said second piston and hence said gripping means until said first piston and hence said expanding means move rearward said predetermined distance, thereby preventing rearward movement of said second piston and hence said gripping means in situations where said gripping means fully engages a tube to be pulled before said first piston and hence said expanding means move rearward said predetermined distance, whereby tube-pulling operations are automatically aborted in such situations to prevent damage to a tube sheet from which a tube is to be pulled.