●The lock-up valve is used if any air source or air supply piping line
  failure occurs in the air operated process control line
  Single acting, Double acting: Retains pressure at the operating area
  as emergency operation until the air source is recovered to its normal state
  3 Port: Changes the supply port if a trouble occurs

Field	Value	Value Details
Action	211	Double Acting
Thread Type	N	NPT
Port Size	02	1/4
Accessory	-	None
Suffix	SL	External Parts Copper-free/Low Temperature (–30 To 60°C)