As Emp` pointed out, pev_gravity from what I've seen is just a scale based on sv_gravity. For example, if the server gravity were to be 800 and an entity/player's pev_gravity would be 1 they would act according to the server's gravity value of 800. However, if you had pev_gravity set to 0.5 that would be half of the server gravity or 2 for double.