Movement of lymph through the lymphatic system?

Question

What causes this?

Answer 1

"The lymphatic system acts as a secondary circulatory system, except that it collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due to peristalsis, the operation of semilunar valves in the lymph veins, and the milking action of skeletal muscles. Like veins, lymph vessels have one-way, semilunar valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins."

Answer 2

The lymphatic system runs parallel to the circulatory system and is not connected to the heart. Lymph moves when the lymphatics are compressed by muscle contraction.

Answer 3

The lymph vessels don't have a heart that moves fluid through them. Instead, the vessels have a series of 1 way valves and your regular muscle movement pushes the fluid up and up. Some people's feet become swollen if they sit to long (like on an airplane). This is from fluid build up due to inactivity.