through gas liquid 23 and then arrive at the bottom of tubing 16 motor valve 42 is then opened to communicate tubing 16 with production line 38 and plunger 22 rises a height of liquid slug 23 in the bottom of tubing 16 may be determined from the following equation height of liquid ft cp u2212 tp psi 0 433 psi ft u00d7 spgr of liquid control of the size of liquid slug 23 can occur earlier in the plunger cycle and can occur more than the 2 times illustrated in fig5 referring now to fig6 shown are the steps for controlling a liquid slug 23 that is too small during a shut in period of a plunger cycle event 1 indicates well shut in e g by closure of motor valve 42 after event 1 casing pressure cp and tubing pressure tp rise plunger 22 falls through gas then through liquid 23 and then remains on the bottom of tubing 16 for a short period event 2 indicates that tubing pressure is briefly vented to production line 38 fig1 e g by opening tubing valve 32 this action may be taken when the difference between the casing pressure and the line pressure is determined to be too small venting tubing pressure to production line 38 ensures that tubing 16 is at lower pressure than the pressure in annulus 17 of casing 12 i e than the casing pressure if liquids are proximate to the bottom of tubing 16 in casing 12 then the liquids will flow into the bottom of tubing 16 at event 3 of the shut in period tubing pressure.