c . Screw-Type Pumps. A double helical screw-type pump, also called
progressing-cavity pump, will pump cement grouts and other slurries.
Pumps of this type will handle solids in suspension and will pass particles up
to 7/ 8 -in. size, depending on the size of the pump. They have few working
parts and are fairly free from mechanical trouble. They can be driven by
air motors, gasoline engines, or electric motors. Pumps of this type pres-
ently available will operate up to 600 -psi working pressure. Pumps for
higher pressure may be available in the future. The progressing-cavity type
pumps (fig. 15) are suitable for pumping practically all grouts.
pumped by centrifugal pumps. The weak points of centrifugal pumps when
used for this type of service are the seals for the impeller shafts and their
handle large quantities of materials at low pressure.
e. Air Pots or Pneumatic Grouters. An air pot is a cylindrical steel
pressure tank from which grout or other material can be forced by com-
p r e s s e d air. The tank is charged through a gasketed door at the top and dis-
charged through the grout outlet at the bottom of the tank. Taps for air -inlet
and air -exhaust valves and a pressure gage are provided. A small valve-
controlled stream of air is introduced into the bottom of the tank, usually
through the grout outlet, to keep the grout agitated if it cannot be discharged
i m m e d i a t e l y . Grout is mixed in a separate mixer and conveyed through pipe
or hose or mechanically to the grout tank. If only one pot is used, grouting
must be intermittent since movement of grout to the hole stops while the
chamber is being charged. Continuous flow can be provided by two pots, each
having its discharge line connected to the grout line by a wye valve and being
operated so that one pot is charged while the other is discharged. Pots with
twin chambers also provide for continuous injection. The equipment is sim-
ple and can be shop made in an emergent y, or Gunite or pneumatic-
concreting equipment can be adopted as air pots. The principal disadvantage
of air-pot-type equipment for grouting is that the grout in the tank is not vis-
ible and air may be injected into the hole before the, operator is aware that
all the grout is out of the chamber. Other less important disadvantages are:
(1) the maximum grouting pressure depends on the air pressure available,
(2) a double -line grouting system (para 17a) cannot be used, and (3) constant
attention must be given the gaskets on the doors to avoid air leaks.
G R O U T LINES.
a . G e n e r a l . There are two primary arrangements of piping used to
supply grout from the pump to the hole. The simpler of the two is the
s i n g l e - l i n e system. It consists of a pipe or a hose or a combination of both,
extending from the pump to the header (d below) at the hole. The pump speed
controls the rate of injection. The second arrangement is the double -line or
c i r c u l a t i n g system. This system has a return line from the header to the