syringe 10 is shown in fig1 . the syringe 10 is of conventional configuration . it has a barrel 12 in which is slidably - disposed plunger 14 . the plunger can slide within the barrel to receive or dispense fluid therefrom . the barrel carries luer lock 16 thereon . the luer lock comprises a collar 18 which has interrupted interior threads 20 and nozzle 22 which extends past the collar 18 . nozzle 22 is tapered and has an interior passage 24 which extends into the interior of the barrel . thus , depression and retraction of plunger 14 moves fluid through passage 24 into or out of the syringe barrel . this is conventional construction . the retractable hypodermic needle assembly of this invention is generally indicated at 26 in fig1 , 2 , 3 , 4 , 5 , 6 , 7 and 8 . it comprises a body 28 . in the right hand of the body is formed tube 30 which carries fingers 32 . the fingers are configured to enter into the collar 18 and engage on the interrupted threads 20 therein . it is these fingers which retain the needle assembly 26 on the syringe 10 . this is common luer lock construction . the other end of the body 28 carries needle sheath 34 . the needle sheath is a tube which slidably carries the needle 36 therein . the needle sheath terminates in a blunt end 38 . the needle has a diagonally - cut sharp end 40 . the sharp end is retracted into the needle sheath 34 in fig4 and is extended in fig5 . the needle 36 extends backward through the body 28 . within the seal cavity 42 , within tube 30 , spring stop collar 44 is part of the needle . compression spring 46 surrounds the needle , engages against the spring stop 44 and lies within the spring pocket 48 in body 28 . the spring urges the needle to the right , retracted position shown in fig4 . to the right of spring stop collar 44 , elastic ball 50 engages around the needle tube . in the retracted , right - most position of the needle seen in fig4 , ball 50 is engaged against circular lip 52 which surrounds the right end of seal cavity 42 . the ball engages against the interior of the seal cavity , engages against the outside of the needle tube and engages against the spring stop collar 44 , as shown in fig4 . the ball serves as a retracted position stop for the needle , when it is withdrawn into the sheath by compression spring 46 as shown in fig4 . this is a safe position where the sharp end 40 of the needle is withdrawn into the sheath 34 . the needle will stay in the retracted the needle assembly 26 is assembled onto the luer lock of syringe 10 . as seen in fig5 , the nozzle 22 of the syringe engages against the ball 50 and presses the ball leftward in the seal cavity 42 until it engages against the left end of the cavity . at this point , the stop collar 44 is at the entrance of the spring pocket 48 . in this position the sharp end 40 of the needle 36 extends past the blunt end 38 of the needle sheath 34 . the hypodermic syringe and the needle assembly are now ready for insertion and injection . immediately after injection , the needle is withdrawn from the patient . thereupon , the needle assembly is removed from the syringe . upon removal , the nozzle 22 no longer holds the needle to the exposed , left position , but the compression spring 46 moves the needle 36 and ball 50 to the right to the retracted position shown in fig4 . now the needle is thrown away . as soon as the needle is retracted into the sheath , the needle is safe . the various dimensions can be established in accordance with the amount of needle exposure which is required . only the needle touches the patient , and as soon as the tip of the needle is retracted into its sheath , the needle is safe . fig6 and 7 illustrate a structure where the retractable hypodermic needle 26 of this invention is used in connection with a phlebotomy set 54 . the phlebotomy set is configured for the direct withdrawal of blood from the patient to a blood collection tube 56 . the needle holder 58 of the phlebotomy set is of similar configuration to the syringe barrel 12 . it carries a nozzle 22 with a luer lock thereon which is the same as the luer lock 16 on syringe barrel 12 . the difference is internal of the phlebotomy set and does not affect the operation of the needle assembly 26 . the blood collection tube 56 has an elastomeric cap thereon and the blood collection tube has a vacuum therein . the blood collection tube may contain chemicals for preserving the blood or for other purposes with respect to the blood . thus , the blood collection tube 56 is an independent structure . interiorly of the needle holder 58 is a tubular needle directed toward the blood collection tube 56 . the interior tubular needle is in line with and is connected to the nozzle 22 and its passage 24 . the phlebotomy set is used by placing the needle assembly 26 on the needle holder 58 . this extends the needle tip from the needle sheath 34 as shown in fig7 . the medical person then inserts the needle into the vein . when in position , the blood collection tube 56 is thrust down into the needle holder 58 . thereupon the puncture needle in the needle holder punctures the rubber cap on the blood collection tube 56 . the vacuum in the blood collection tube withdraws blood from the patient , through the needle , through the sealed luer connection , through the puncture tube into the blood collection tube . the hypodermic needle must be first inserted into the patient , before the advance of the blood collection tube so that the vacuum in the blood collection tube is not lost due to premature puncturing of its cap . after the collection is completed , the blood collection tube 56 is removed from the needle holder and the needle assembly 26 is removed from the needle holder . the removal of the needle assembly withdraws the needle 36 into its sheath 34 . thereupon , the needle assembly can be disposed . the blood collection tube goes to the laboratory and the needle holder can be sterilized for re - use , or disposed . the needle assembly 26 can also be used with an intravenous drip tube , as shown in fig8 . the intravenous tube 60 comes from an iv fluid bag and through a dispensing pump . the end of the iv tube is provided with a luer lock 62 , the same as the luer lock 16 . when iv fluid is to be administered , the needle assembly 26 is attached to the luer lock 62 . this extends the needle 36 out of its sheath 34 so that the needle can be inserted into the patient &# 39 ; s vein . the system remains in place until completion of the fluid transfer . thereupon , the needle is withdrawn from the patient and the needle assembly is released from the luer lock . the release from the luer lock permits the spring to withdraw the needle into its sheath , therefore protecting personnel against inadvertent needle sticks . an effective protection of needles has been created . this invention has been described in its presently contemplated best modes and it is clear that it is susceptible to numerous modifications , modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty . accordingly , the scope of this invention is defined by the scope of the following claims .
a needle assembly includes a sheath into which a hypodermic needle is withdrawn in a protected position . installation of the needle assembly onto a luer lock causes the needle to be thrust forward out of the sheath . a spring urges the needle to the withdrawn position . an elastomeric ball in the needle assembly provides sealing .