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Making a strong “ head-works ” for

the Zimbabwe Bush Pump

(for boreholes)

Peter Morgan



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Introduction

The “head - works” (the concrete apron and water run-f f and soak-away system, is a vital part of any

Bush Pump install ation. M ost boreholes are now dri ll ed with a diameter of 150mm and cased with aPVC casing ranging in size from 125mm to 140mm (OD) (preferably class10). The smal ler casing size

is sur rounded by a gravel pack. The upper part of the PVC l in ing is sur rounded by a stout steel pipe

(known as a “short casing” ) f i tted with sprags which are embedded in a block of very strong concr ete.

This block is covered and bonded with an equally strong disc of reinf orced concrete which forms the

apron. Th is has a raised rim. Water f all ing on the apron then f lows down a water r un-off in to a soak-

a-way system.

The concrete apron has several functions.

1. I t shoul d prevent pumped water passing back down into the borehole

2. I t shoul d securely and r igidly hold the steel casing whi ch supports the pump head3. I t should dir ect waste pumped water away from the immediate site of the borehole

I n the case described in this manual, the 150mm diameter steel pump support pipe (“short casing” )is

80cm long and f it ted with sprags to secure it to the concrete support. Steel shuttering is used to form

the concrete apron and run off . A 60cm x 60cm square hole is dug down 20cm below ground level

around the PVC casing (which protr udes 50cm above ground level). The 80cm shor t casing is then

lowered over the PVC casing and the 60cmx 60cm x 20cm deep hole is f i ll ed with strong concrete.

The concrete mix i s 3 parts 20mm stone, 2 parts river sand and 1 part cement (PC15). The shor t

casing i s made vertical.

The apron and water run-offThe construction of the apron then begins. Th is has a diameter of 2m and th ickness of 100mm. The

water run- off is 2.5m long. The outer rim of the apron is raised and is 10cm hi gh and 75mm wide. I n

thi s case the apron and water run-off system i s made using steel shutteri ng. Both outer and inner

shuttering are used. The outer shuttering is laid around the shor t casing, so the casing is about 50cm

from the rear edge of the apron. The shor t casing should r ise 50cm above the concrete apron.

A l ayer of strong concrete is then laid inside the outer shutteri ng and water run-of f shutteri ng 10cm

thick. Half of this thickness is added fi rst, then a gri d of steel mesh (4mm thick)wi th 150mm spaces is

added and cut to f it the apron and run-f f The remaining 5cm of concrete is added to make the ful l

thi ckness of the apron 10cm. Af ter the concrete has started to harden a l it tle, the inner shuttering is

then laid with in the outer shutteri ng and a fur ther strong mix of concrete is poured between the inner

and outer shutters to make the rim of the apron. This is 10cm high and 75cm wide. A slight sloped is

made on both apron and run of f so water wi ll run clear of the apron and down the run -off into the

soak-a-way.



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The concrete is left to harden and then the shutteri ng i s removed. A f inal layer of strong plaster is

laid over the apron and water run-ff to make a smooth coveri ng and one which is sloped to allow

complete water drainage from the head-works.

Using this techn ique the steel support pipe is embedded in 30cm of strong steel rein forced concrete.

The shor t casing rises 50cm above the level of the concrete apron . When the bush pump is f it ted theheight above the apron is suf f icient to al low a 25li tre plastic container (chikube) to f it beneath the

pump water outl et pipe. The concrete apron must be kept wet to cure for at least a week before the

pump is f itted and put to use. Thi s wil l all ow the concrete to cure properl y. I f the pump is f it ted before

the concrete is cured the steel suppor t pipe wi ll become sl ightl y loose, forming a space between

concrete and casing through which waste water can drain back into the borehole. This f low can

pollu te the ground water enteri ng the casing.

The rear r ubber bufferAn addit ional requirement i s also required. This is the inserti on of a stout car tyre in the ground

behind the head-works. Thi s tyre is dug hal f way in to the ground in a posit ion where the pump handle

wil l come to rest on the tyre on the extr eme down stroke. Th is acts li ke a buf fer for the handle on thedown strong. The rubber buf fer f it ted above the floating washer housing of the pump acts as buff er

for the rod system on the down stroke. When buf fers are f it ted on both up and down stroke the pump

suf fers less fatigue duri ng use. The length of the stroke can also be controll ed. The rubber tyre is

f it ted at the same time that the pump is f i tted, so that the distance between pump and tyre can be made

accurately. The rear end of the pump handle should come to rest on the tyre to form a buff er on the

handle down stroke.

The soak-a-wayThe soak-a-way system is made at the end of the water run -off i n the form of a ring beam (bri cks or

concrete) with a hole dug down at least 60cm beneath the beam. 40cm+ is fi l led with course river

sand and a fur ther 20cm with gravel or granite chips. The size of the soak-a-way vari es depending onlocal condit ions. I t may require enlargement in areas of di ff icul t drainage or where the pump is used

by large numbers of people. Good drainage if far more diff icul t duri ng the rainy months.

The construction uses between 5bags of PC15 cement, approx 0.5 cu.m. of river sand and 0.75cu.m.

of 20mm stone. Some pit sand is also requir ed for plasteri ng. The unit is rugged and perf orms the

special requi rements of a Bush Pump head-works.

Peter MorganFebruary 2012

AcknowledgementsThanks are due to V&W Engineering f or providing the shuttering, materials and labour for the

construction of th is demonstrati on unit.

A publi cation by Aquamor



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Annotated photos of the construction

The borehole is dri l led to the desir ed depth and a PVC casing (slotted at the lower end) sur rounded by

a gravel pack is inserted. The PVC casing (class 6 – preferabl y class 10 ) extends 50cm above the

ground level. Photos show 125mm PVC surrounded by gravel pack and the 80cm long steel pumpsuppor t, which wil l be placed around the PVC pipe to support the pump head.

A 60cm x 60cm hole is dug down 20cm below ground level around the PVC casing and the steel pump

suppor t pipe is lowered around i t and made vertical. Th is pipe is fi tted with sprags whi ch are 10cm

from the bottom of the pipe. A view of the steel pipe f i tted around the PVC pipe.

A strong mix of concrete (3 parts stone, 2 parts river sand and 1 part PC15 cement) is mixed. Using a

bui lders bucket, hi s fir st mix contains 3 buckets stone,2 buckets sand and 1 bucket cement. The

bui lders bucket contains 15 li tres of material. The 4 sprags are complexly covered with 10cm concrete

below and 10cm concrete above the sprags.



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The method shown here uses steel shuttering designed specif ically for this purpose. The shuttering

has an inner and outer shell . The outer shell is laid down f ir st. The area around the borehole site is

leveled fl at and the outer shuttering laid around the borehole. A 10cm deep layer of concrete wil l be

laid with in the shuttering to make the apron of the head works. The shutteri ng is placed around the

borehole so that the borehole is about 50cm from the rear of the shuttering. Water wil l then f low f rom

the pump to a posit ion near the middle of the apron. The shuttering is bolted together as shown.

The shuttering uni t has an apron diameter of 2m and a water run -off channel length of 2.5m.A seri es of shout pins are placed around the shuttering uni t to keep in place.

A large volume of concrete is then mixed. In th is case the 3:2:1 mix of stone, river sand and cement is

retained as the ideal mi x. Using a builders bucket (15 li tres), 21 buckets of stone, 14 buckets of sand,

and 7 buckets of cement are used. A bag of cement contains a li ttl e less than 3 buckets of cement

(about 42 l itr es).



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The soil around the borehole and down the water run-off , withi n the shuttering is wetted down

The concrete is then poured inside the shuttering (apron and run-of f section) to a depth of 5cm and

leveled off .

A piece of weld mesh (4mm wi re with 15cm spacing) is then laid over the apron area and around the

steel pi pe and down the water runof f channel. I t is cut to sui t the shape of the head-works.



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More concrete is then laid over the weld-mesh to make a total thi ckness of 10cm throughout the head

works area. This is leveled flat and smoothed down

The apron and water run-of f base concrete work. The inner shutter is then laid over the concrete to

make the rim of the head works

Spacer bars are part of the head-works shutter ki t and ensure that the width of the rim wall is 75mm.

The height of the rim wall is 10cm.



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The space between the inner and outer shuttering is now f il led with concrete to the upper level of the

shuttering. The same 3:2:1 mix of stone, sand and cement is used.

Once the concrete work has been completed, the mix is lef t to set and cure. The shuttering i s removed

after 24 hours and cleaned

The apron and water run-off after the shuttering has been removed. The concrete is lef t to cure and

strengthen f or at least one week before the pump is f i tted. The entire concrete work is plastered to

ensure a slop which al lows wat er to completely drain the unit. The length of the “short casing” above

the concrete should be 50cm.



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F itting the rear rubber buffer

The Bush Pump head is fi tted with a rubber buff er f or the down stroke and i t is advisable to f it one

for the upstroke too. This can be made using an old car tyre which is inserted in the ground at the

rear of the apron. The handle comes to rest on the car tyre. This avoids the end knock whi ch occur s if

the handle comes to rest on concrete or on the ground. The stroke length of the pump can also be

more accurately def ined if there is a stopper for the handle. I f the Bush Pump is mounted too high

above the ground, the handle may pass beyond the recommended angle of operation.

Digging the hole for the tyre and inserti ng the tyre in the correct place

Fil li ng the lower part of the tyre with rubble. Back f il li ng with soil and ramming hard



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The Soak-a-way

The soak-a-way is an important part of the head-works system and al lows waste water to dissipate

in to the ground away from the immediate posit ion of the borehole. Very often soak-a-ways are holes

filled with rocks, but these may be less effective. The systems used here is in the form of a “ring

beam” of bricks or concrete placed at the end of the water run -off . I n the case il lustrated this is 1m indiameter. A hole is dug down at least 60cm inside the ring beam. Much of thi s depth (40cm+) is f il led

with course river sand and the upper 20cm + with granite chi ps (the same as used to make the

concrete). The actual diameter of the soak-a-way wil l depend on the soil type and drainage condit ions

and also the number of users. Good drainage of spilled water is often very difficult to achieve,

especial ly i f the soil does not drain well and during the rainy season when the top soil is saturated and

also when a large number of people use the facil ity. The soak-a-way system shown here may need to

be extended through a “herring bone” system to increase the area of the soil/sand interface. Also the

soak-a-way system may require digging out with replacement sand being added fr om time to time.

The end of the water r un-off . A r ing of bri cks is laid down. I n th is case about one metre in diameter.

The bri cks are bonded together wi th strong cement mortar . A hole is dug down inside the ri ng beam

60cm deep. The lower half is fi ll ed with ri ver sand and the upper half with grani te chips. Also the

apron and run -off should be plastered with a strong cement plaster mi x to ensure a good slope

towards the soak-a-way. The exact dimensions of the soak-a-way wil l depend on l ocal condi tions (soil

type, number of users etc).



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The hole within the ring beam is dug down to at least 60cm and almost completely f il led with very

course river sand. Th is wil l reduce the side wall erosion of the seepage pit.

A layer of course stones, granite chips or gravel is placed over the course ri ver sand. Photo on r igh t

the completed head-works with pump attached.

Summary

The head-works of any Bush Pump installation is a vital part of the enti r e assembly

and should be constructed proper ly fr om the start. I t shoul d be remembered that i f the

pump is fit ted prematur ely (that i s before the concrete has had time to set and cure) the

casing wi ll move within the concrete, no matter how strong the concrete is made. A

period of at least a week should be left between completion of the head-works and thefi tting of the pump itself. Also maintenance of the head-works is requir ed. The soil

around the head-works has a tendency to erode away, partl y as a resul t of rain and

partly because the area is heavi ly used. Topsoil should be replaced around the head-

works. The soak-a-way system wi ll also need attenti on depending on local conditions

and use.



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