The       states that the operation of any piston pump is based on the relative motion between the piston and the cylinder. It follows that if the plunger is stationary and the barrel moves, the same pumping action is achieved in the rod pump. The moving barrel rod pump operates according to this principle and the plunger remains in place as the barrel moves through the rod. The position of the anchor or the compression member is always at the bottom of the pump assembly.

　　

The mobile cartridge pump is versatile and can be used for normal, sandy and corrosive wells. The plunger is connected to the bottom compression tube through a short hollow pull tube through which the well fluid enters the pump. The size of the upright valve at the top of the plunger is less than the size of the travel valve. The thin wall pump is designated RWT with a flexible package plunger RST.

　　

When sand production is a problem, mobile bucket pumps are widely used; their main advantages are as follows.

　　

The moving barrel keeps the fluid moving around the hold down device, preventing sand or other solids from settling between the seat joint and the hold down device. Therefore, the pulling of the pump assembly is generally trouble free.

　　

It is recommended that the pump be used for intermittent pumping of manholes because sand cannot enter between the plunger and the barrel during shutdown.

　　

The connection between the pole and the moving cylinder is stronger than the connection between the stem and the pole in the fixed cylinder pump.

　　

It is rugged and has fewer parts than a fixed barrel pump and is less expensive.

　　

The disadvantages of walking pumps are:

　　

The size of the vertical valve is limited because it must be loaded into the barrel. This relatively small valve provides high resistance to fluid flow, allowing gas to separate from the solution, resulting in poor pump operation in the gas well.

　　

In deep wells, the high hydrostatic pressure acting on the upright valve during the downstroke may cause the pull tube to bend and excessive wear between the plunger and the barrel. This limits the length of the bucket that can be used in deep wells.

　　

Pumping high viscosity fluids is not recommended as small standing valves can cause excessive pump inlet pressure.