The illustration, Fig. 22, shows a machine of this type. The same methods are used to operate this kind of machine as are used with the single action with this exception that there must be two lifting levers, either overhead or cradle levers. The reason for using this kind of machine is to have an open shed motion, and to gain a little extra speed; but this naturally drives the cylinder faster, consequently there is a greater damage done to the cards unless great care is taken with them and additional appliances used to prevent them from jumping off the pegs.

The needles and hooks used in this kind of machine are shown in Fig. 23. Each needle has two eyes or curves. The reason for two eyes is as follows: There is but one cylinder and two griffes, one of which is descending while the other is ascending. The cylinder has to pass in for every pick; that is, for each lift of the griffe, which necessitates the use of double the number of hooks; so that in a 400-machine, there are 800 hooks, without the extra ones. The top bend of every hook is turned in the same direction, that is, toward the needle board.

The hook that is used on this machine requires a deep bend at the top so as to have a firm grip on the griffe blade. This is necessitated by the method of controlling two hooks with one needle, for it sometimes happens that one hook is lifted while the other is pressed back by the cylinder, so that the same thread will not be lifted for the next pick.

The bottom of the hook is made in the form of a capital letter V. The reason for this is that it saves a considerable amount of friction by allowing the bottom of the hook that is lifted to move back a little as the “partner” hook is being pressed by the needle. This shape of hook saves the grate through which the bottom of the hook passes. Fig. 23 shows the position occupied by the hooks when one hook is lifted and the other hook (which passes through the same needle) is pressed off. The dotted lines show the original positions of the hooks.

In addition to the added friction on the needles and hooks, it takes considerably more time to replace a worn needle than it does in machines where single needles are used, for a rod has to be temporarily inserted that will press to one side the two hooks around which the needle has to go, and it is often necessary to take out the hooks until the needle has been replaced, particularly if the machine is an old one, or if deep blades are used in the griffe.