This listing is for one pale yellow valve & white membrane. The yellow valve holds the white membrane in place. They provide a filter, and are an integral part of the suction apparatus. The yellow valve and white membrane should be removed each time the pump is used. The white membrane should be removed from the yellow valve and each cleaned separately. This prevents debris from being caught behind the white membrane and also prevents the white membrane from sticking, which can lead to decreased suction.
If you wanted to purchase a different amount you can purchase a larger set, or the valve and membrane individually.