The delay valve that allows vac from the engine to the transmission is a switch-over-valve and is the Delay Shift Valve..
It, like all SOVs , is a Valve that , when electrically energized,
opens -allowing vac flow.
The working part on the trans is a Vac. Actuator [ sometimes called a vac element/servo]
It is not a valve in the sense that a valve allows flow...
The actuator mechanically moves a cable[ actuates] to a set position to retard the shift point.. and it does this when the Delay valve lets engine vac reach it.
So, if one test for vac on both sides of the delay valve, from there you can tell if the Acuator is getting vac and is at fault , or if the SOV is not allowing vac to reach the actuator....
This may help one understand the system...