There is no way to answer that with the information you gave.
IF the motor is single phase AC, AND the relay in question has a motor RATING that is at or greater than the motor kW / HP in question, then it would not matter if the relay was single pole or double pole. For a single phase motor, all that is necessary to start and stop the motor is to break one of the line power leads. Protection for the motor is not part of what a relay does, so all of that is separate.
IF the relay does not have a rating in kW or HP at least equal to or greater than the motor rating, you cannot use it. This is not as simple as just matching the motor FLC to the maximum current rating of the relay, the MOTOR rating is different because it is much harder of the relay contacts. Without that induction motor rating the contacts could weld and the motor may not be able to be stopped.
IF the motor is 3 phase, then you must break at least TWO of the 3 power leads, and you MUST use at least a double pole relay.
If the motor is DC, the relay must have a DC rating at the voltage you are using, which in the type of relays described as SPST or DPST, is unlikely.
Valves are less complicated, but the same issues of ratings apply because a valve coil is still an INDUCTIVE load, so the relay contact rating must be in watts, not just amps.