Landfill pump having metered cycling

A landfill pump for pumping a liquid out of a wellbore in a landfill, the landfill pump comprising:

• a case, the case cylindrical and elongate along a pump axis;
• a pump chamber located at least partially within the case;
• a manifold disposed at a top end of the case;
• a liquid inlet, the liquid inlet configured to permit the liquid to flow from outside of the landfill pump within the wellbore and into the pump chamber;
• a liquid inlet valve that opens to allow the liquid to flow from the liquid inlet into the pump chamber and closes to block the liquid in the pump chamber from flowing back out of the liquid inlet;
• a liquid outlet channel at least partially formed through the manifold and through which the liquid is discharged;
• a liquid outlet valve that opens to allow the liquid to flow out of the pump chamber through the liquid outlet and closes to block the liquid from flowing through the liquid outlet and back into the pump chamber;
• a discharge pipe that extends axially within the casing and within the chamber, the liquid outlet channel extending at least partially within the discharge pipe;
• a valve assembly configured to regulate flow of a compressed gas into the pump chamber to force the liquid within the chamber out through the liquid outlet;
• a float that rises and falls within the pump chamber in response to changing levels of the liquid within the chamber, such movement of the float actuating the valve assembly between a fill state and a discharge state, the valve assembly admitting the compressed gas into the pump chamber in the discharge state and the valve assembly blocking admission of the compressed gas into the pump chamber in the fill state;
• a control rod interfacing with the float, wherein the float is configured to rise within the pump chamber with a rising liquid level to cause the control rod to actuate the valve assembly to the discharge state, and the float is configured to fall within the pump chamber with a falling liquid level to cause the control rod to actuate the valve assembly to the fill state;
• and
• a pneumatic outlet channel configured to vent the compressed gas from the chamber, wherein a choke is located along the pneumatic outlet channel to slow cycling of the landfill pump by slowing egress of the compressed gas from the pump chamber and consequently slow ingress of the liquid into the pump chamber;
• wherein the landfill pump is configured to undergo a plurality of pump cycles, each pump cycle comprising a filling phase in which the liquid flows through the liquid inlet into the pump chamber and an evacuation phase in which the valve assembly causes release of the compressed gas into the pump chamber to force the liquid out through the liquid outlet channel;
• wherein the choke is formed in a bleed piece connected to the manifold and the choke slows egress of the compressed gas from the pump chamber during the filling phase.

A method of cycling a landfill pump configured to pump liquid from within a wellbore of a landfill, the method comprising:

• admitting a flow of compressed gas into the pump chamber from a pneumatic inlet channel of the landfill pump with a valve assembly of the landfill pump in a discharge state, the compressed gas driving liquid within the pump chamber downward within the pump chamber and then up a dispense tube and out through a liquid outlet of the landfill pump;
• actuating the valve assembly to a fill state, in which the flow of compressed gas to the pump chamber is shut off, by a float falling within the pump chamber with a falling liquid level in the pump chamber;
• and
• restricting an outflow of the compressed gas from the pump chamber by a choke disposed within a pneumatic outlet channel of the landfill pump to slow cycling of the landfill pump by slowing egress of the compressed gas from the pump chamber and consequently slowing ingress of the liquid into the pump chamber.