I am planning to do some minor jacking of the main beam of my house (two stories with a lot of furniture and books) and some of the joists in order to correct a sag of about 1/2" and replace old "timbers" (literally tree trunks) with concrete lolly columns. According to books I have covering this kind of renovation, the recommendation is to use a hydraulic jack (like a 40-tonner) to do a micro-lift, then actually hold it with a screw jack (say a 25-tonner). After the screw jack is tight, you remove the hydraulic jack. Then the next month you put the hydraulic jack back again and repeat the process. You only need one hydraulic jack which can be used to service all your screw jacks.
On the other hand I have read accounts of people doing small jacking jobs and they seem to claim that you can actually lift with the turning bar/screw jack directly and seem to have success without the added help of a hydraulic.
Should I get the hydraulic jack or just try manually using the screw jacks alone first?