Sometimes the jack will become air bound by reason of the accumulation of dirt around the filling plug; this must be removed before the jack will work. Sometimes the liquid will all have been displaced before the ram is half way up, in this emergency the reservoir must be refilled. It often happens that when the workman stops working the lever it will persist in rising to its highest position. This indicates the presence of dirt under the lower or delivery valve. One or two sharp quick strokes of the lever will generally dislodge such obstructions; if this does not bring relief the valve is probably worn so as to need regrinding. _When a jack has been taken apart each part should be thoroughly washed in clean water._ While using, _if the liquid escapes over the top of the cylinder_ the ram packing is too loose, and may be set out by inserting a strip or strips of tin or any sheet metal between the leather and the ram packing ring; all leathers should be kept soft and pliable by saturating with a proper leather dressing such as Frank Miller’s Leather Preservative or Shoemakers’ Dubbing. Castor Oil is excellent as well. _One man can exert upon the lever_ all the pressure that the jack is capable of raising and this pressure should not exceed 150 lbs. Beyond this the jack will be strained. _To repack the pump_ remove the pump plug, and unscrew the set screw in the head, then withdraw the socket far enough to permit it to revolve clear of the lug, on the head, which brings the piston head out of the pump. After the new packing is in place the piston should be worked in and out a few strokes to see if it is right, then replace the plug. _To fill the reservoir_ remove the filling screw in the top of the head, and fill with a mixture of proof alcohol (95 per cent.), two parts and water three parts for winter use, or for summer use one part alcohol to four parts water. _When not in use_ the ram in a hydraulic jack should be kept in its lowest position, that is to say, all the way down, _or in_, as the case may be. IMPORTANT.—Jacks should never be filled with kerosene oil, water or wood alcohol, for the following reasons: Kerosene oil destroys the leather packing, water will rust the parts and make them rough, while wood alcohol attacks the smooth steel surfaces, and thus destroys both the cylinder and ram. All liquids should be well strained before putting them into the reservoir and great care should be exercised to prevent any dirt from getting into this reservoir. _The Pulling Jack._—The pulling jack, Fig. 139, is used in connection with travelling cranes over wheel presses, quartering machines, planers, drill presses and lathes. Its operation is the reverse of lifting jacks. This Jack has an improved force-pump on the outside, worked by a lever, which draws the liquid from the upper end and forces it into the space on the opposite side of the piston. The piston rod has one of the rings attached at the end.