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Introduction
Booster pumps are widely used
to enhance the performance of a shower. Not all
people like to have water hurled at them at high velocity,
though some prefer to feel as though they've been blasted with a
pressure washer. While there may be some sort of sadomasochistic
force at work with the bigger models, power shower pumps
range in performance and at the entry level offer a means to
turn a disappointing dribble into a worthy event. As
pressure and flow rates increase so does the enjoyment of having your
skin massaged with jets of water. Whatever it is for you
there are a few simple yet important factors to take into
account otherwise you may end up regretting your investment.
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This is where the supply to
the pump emanates from a header tank (also known as a
cistern) often sited in the loft. It is in contravention of
Water Bye Laws to try and increase the performance (pressure
or flow rate) of a system directly fed from the rising main.
More specifically...
If you have a mains pressure
hot and/or cold water system you may not add a pump
in an attempt to make it more powerful (this is why you
should be mindful of your supply pressure and flow rate when
opting for a mains pressure system. You do not have the
option of boosting supplies should you subsequently discover
they're not to your satisfaction.)
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You must not attempt to
increase performance by adding a pump ahead of the boiler
(to increase incoming pressure and flow which is fed
directly from the main) or after the boiler to enhance
output (this won't work and it is in contravention of Bye
Laws being a mains fed device). As the boiler is already
working at maximum output there is little point trying to
make it work harder.
Furthermore...
Booster pumps are designed to
take a 'low pressure' feed and boost it. The pressures that
can build up in a mains supply (especially at night when
water demand is typically low) can be high and are likely to
blow seals. Connecting your pump to a mains supply will
invalidate its warranty.
A gravity water system (that's
one fed from a header tank) is the ONLY type of water system
to which you may fit a booster pump. For various reasons you
may not fit a pump to any other sort of system. Installing a
booster pump to a gravity supply will normally increase the
water pressure substantially, but you should consider what
sort of pump to buy carefully based on your shower equipment
and more importantly... your expectations.
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Many households have to deal
with what we shall call a 'split system'. This is where hot
water is supplied under gravity pressure and all the cold
water outlets are at mains pressure. In the old days when a
separate tap dealt with each you wouldn't necessarily have
noticed. But nowadays it is very common to find mixer
showers in many bathrooms and this is where a problem begins
to manifest itself. |
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When you supply a shower mixer
valve with unequal pressures you may experience difficulty
controlling the output temperature. This can be due to the
overwhelming nature of the mains pressure cold supply in
comparison to the relatively weak supply of gravity hot
water.
Water has a single objective -
to find the easiest route out. So when the higher pressure
cold water hits the shower valve it is presented with a
choice - to exit via the valve and handset or go back up the
hot water pipe (which can often be the easier option). You
can probably appreciate if the latter happens you won't get
any hot water.
Attempts are made to cure this
problem by simply boosting the pressure of the hot water.
Logically one might consider this a sensible option.
Although there is nothing wrong with boosting just the
gravity supply it frequently fails to address the problem
fully. The reason? You need to consider what happens when
you open the shower valve. (The diagram to the right
illustrates such a setup) |
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When both feeds (H & C) to the
shower valve are pumped gravity supplies the shower pump
recognises an initial pressure drop or flow of water
as the valve is opened and responds by energising the pump.
However, when the cold water is at mains pressure, the
moment you open the valve the more boisterous cold supply
muscles it's way back along the hot water pipe (seeing this
route as an easy way out) and confuses the pump sensor.
Being unable to recognise valid start up conditions the pump
fails to energise.
It must be said that a twin
impellor pump with a gravity hot and cold supply is by far
the best solution, but if you have been lumbered with the
split system you can get it to work by being a bit tricky
yourself.
You need to protect the
pump/hot water feed from the initial surge of cold water
entering the shower valve. To do this you might try opening
the shower flow control while the temperature dial is fully
in the 'hot' position. This should prohibit cold water from
entering the valve when you initially open it and allow the
hot water flow hence activating the pump. Once activated the
pump will continue to run as you introduce your cold water
to the mix. You should however be very careful! It is
essential that you return the shower valve temperature
control to a comfortable level immediately after the pump
energises. Forgetfulness or failure to do so could result in
scalding.
It is stressed this is not a
recommended fix, it is a way to cheat the system. It is
potentially risky, could result in injury and may not work
in all scenarios. It is recommended you do the job properly
and install a twin impellor pump.
Split or mixed systems are not recommended.
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The ratings by which
manufacturers sell their pumps can be confusing. After all,
when looking at two different pumps each rated at 1 bar
('bar' is the unit by which pressure is expressed. It is
equivalent to 1 atmosphere, 14.5 psi or the pressure that would be
generated by a water tower if it were 33 feet in height)
what is the difference? Why should one be more expensive
than the other?
Bar pressure is only one
component of a water delivery system. It is important to
take into account another crucial factor when examining pump
performance.... the amount of water the pump can deliver
(usually expressed in 'litres per
minute') at the stated pressure. This is known as the
'flow rate'.
For example: 18 litres per
minute (18 l/m or
18 lpm) at 1 bar.
You should not get carried
away by the fact that a pump can simply produce high
pressure. An example of this might be
the little pressure washers you can buy at hardware stores
for cleaning patios, cars, windows etc. These are often
rated at quite phenomenal pressures (1000-1500 psi or pounds
per square inch). Pressure like this could injure you if you
were to direct the blast at your skin. Whilst high pressure,
these little units actually only shift a very small amount
of water. Compare them to the blast from a fire engine hose
- at much lower pressure a fire hose can knock a man off his
feet. This is because of the volume of water combined with a
moderate pressure. The fire engine by maintaining a very
high flow rate at a moderate pressure produces impressive
force/performance.
This, together with certain
other factors, is why one shower pump might cost
more than another.
In defence of pump
manufacturers, specifying what a pump might be able to do is
complicated by another variable - what you are feeding the
water through. For example: A pump feeding water down a hose
at 2 bar without having a nozzle on the end will surely get
your garden wet but you will notice that the water runs
rather than blasts out. Now put your finger over the end of
the open hose pipe and you'll feel pressure build. At the
same time the previously mundane flow becomes a powerful jet
that can reach quite some distance.
Without going into this
further, it is this principal a shower handset exploits -
lots of small holes creating back pressure through which
water is forced. Different handsets will have different
sized holes, some will have multiple spray patterns. This is
why it's so difficult to be exact about how a particular
pump will perform - it's all relevant to what you hook it up
to.
If you have a 'watering can'
or 'deluge' type shower head you cannot expect the same
invigorating performance you might get from a handset. Using
the above example, you are creating less back pressure
because the larger holes in the head are arranged across a
wider area and may be more numerous. This configuration will
get you very wet but you may not get the powerful force you
were hoping for.
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Most shower booster pumps
operate by the same principle. Low pressure water is taken
into a chamber and fed into the centre of an impellor which
is spinning quickly. The water is effectively thrown outward
by centrifugal force and ejected from the impellor housing
at high speed. The amount of water that the impellor can
move determines the flow rate, the force that the impellor
can maintain relates to the pressure. A pump typically has
one or two impellors, depending on whether it is deemed
'single' or 'twin'. Impellors are driven by a motor (usually
electric). A twin impellor pump will often have an impellor
located at either end of the electric motor's armature
(motor positioned centrally).
The power that the motor can
generate will be proportionate to the resulting pressure and flow rate
achievable. A twin impellor pump usually takes a hot and
cold low pressure feed and boosts them simultaneously. A
single impellor pump is suitable for a hot, a cold or a blended
low pressure supply. Most shower pumps are set up to sense
when you open your shower valve and activate automatically.
Similarly, they switch off automatically when you close your
shower valve.
This is a term that you may
have come across but misunderstanding still exists to
exactly what it all means.
In a nutshell, the difference
between the two is determined by whether the header tank is
above or below the outlet point. If the header tank is above
you have a positive head. If it's below the outlet you have
a negative head.
In a gravity water system it
goes without saying that water will only travel in the
direction of gravity - downward. For this reason some people
believe that if you take water down from the loft to a
ground floor hot water cylinder, then back up to a first
floor bathroom that water is indeed having to go up hill and
that a negative head scenario exists. In this example this
would be an incorrect conclusion. It is the relative
position of the header tank to the outlet point. If the
header in the loft is higher than the outlet point then a
positive head exists even though the water travelled down to
the ground floor before going back up to the outlet.
If indeed the outlet is higher
than the header tank and a negative head exists you will
require what's known as a negative head set up.
In a negative head scenario
things kind of happen in reverse. When you open your shower
valve (or outlet - which could be a tap) water would rather
run backward down the pipe to the header tank. SO... if you
want your pump to activate automatically it needs to be
equipped with a different type of sensor. Negative head
pumps can usually be recognised by a canister that
piggybacks the pump. This is part of the sensing system -
not needed on positive head pumps. Alternatively, some
manufacturers supply (as optional extras) what they call a
'negative head kit' or a 'manual negative head kit'. In
reality this kit is nothing more than a manual means of
switching on a standard booster pump when water is required
at an outlet above the header tank. The negative head kit
typically comprises a 'momentary contact' pull chord which
energises the pump. Once running the pump will continue
pushing water up to the outlet until closed, at which time
the pump will turn off - ready for the next manual
activation.
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Other things to know about
power shower pumps.
Apart from
bar pressure and flow rate there is one other fairly major
consideration. Is the pump rated for constant or
intermittent use? Some manufacturers dress this up with
words like 'regenerative', but at the end of the day it all
means the same thing. A pump will either run continuously or
it needs to rest after about 10-15 minutes of use (for about
45 minutes to cool down). If you happen to be a household
where mum, dad and all the children like to use the same
shower one after the other, and the typical shower time will
be from 5-10 minutes, then a pump with intermittent rating
simply won't suffice. When such a pump has been in operation
for it's prescribed time it will simply cut out (so that it
may cool down). Many an unwary owner has thought their
shower pump to be faulty when in fact it is doing what it
needs to do. So, select a pump with a duty cycle that will
match in with your requirements.
We
mentioned in an earlier paragraph about pressure and flow
rate. Focussing on flow rate you should ascertain the size
of the pipe connections on your proposed purchase. Shower
booster pumps typically have either 15mm or 22mm pipe
connections. A 22mm pipe has the capacity to transport twice
the amount of water than a 15mm will carry. The size of
connection is therefore a bit of a give-away as to the
pump's capability. It is not generally considered a good
idea to try installing a pump with 22mm connections into a
system where the rest of the pipework is 15mm.
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As mentioned, both the hot and
cold feeds to a booster pump need to be gravity pressure
supplies. The cold water feed can either be a dedicated cold
supply direct from the header tank, or as is often the case,
by teeing into the cold water feed to the hot water
cylinder. Cold is simple enough. The hot water feed to the
pump needs a little more consideration.
The normal hot water draw-off
point is typically at the top of a hot water cylinder -
right at the top, dead centre. If you simply pull your hot
water from this point you may end up with a problem.
The reason: Hot water releases
minute air bubbles. Ordinarily these rise to the top of the
cylinder and vent out through the header tank in the loft.
If you try taking water at the point where the bubbles are
leaving the cylinder you are likely to pull them into the
pump when it's running. This can cause a condition known as
cavitation. In a nutshell, a big bubble of air forms at the
low pressure zone ahead of the pump impellor. The condition
can cause damage to the pump and will almost certainly
generate some weird and wonderful noises - including
squealing and banging!
The solutions:
1) If you intend to keep the
present hot water cylinder you should consider using either
a 'Surrey' or 'Essex' flange. This device screws into the
top of the cylinder and creates two outlets. One becomes the
normal outlet/vent, the other (being the shower take-off
point) draws hot water from slightly lower in the cylinder,
hence allowing the bubbles to pass on by.
2) If you intend to change the
cylinder for any reason then make sure the new one has a
dedicated shower take-off point. This will do the job of a
flange type device. Shower take-offs shouldn't make the
cylinder any more expensive, but you must ask for one to be
fitted as they are not normally included.
Click here for
more info on cylinders.
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You might really like the experience associated with a
powerful blast of water when taking a shower. Some people
don't feel clean unless they feel a layer of skin has been
removed during the event! But don't lose sight of how
quickly you are emptying your water storage vessels as you
shower.
A boosted shower will empty
your system quicker. The bigger and more powerful the pump
the quicker the system will empty. If you simply add a pump
to your existing system you run the risk of potentially
running it dry unless you do a few calculations. It is
actually quite difficult to be precise with this because of
various factors (how much water for example does your shower
head deliver?). You will need to make certain guesstimations.
The amount of water a shower pump will deliver will even be
affected by how big the holes are in the shower head, and
how many there are! Some how you need to calculate how big
the header tank in the loft must be in order to provide an
average of 10 minutes shower time. Yes, some people
(especially teenagers) stand in the shower for longer, so
you must either make provision for this or re-educate users.
Some people find a timer on the show
it use. Whatever you do and however you choose to do it,
make sure you don't run your pump dry - this can cause it
irreparable damage.
The
materials from which a pump is manufactured will invariably
influence the cost of the pump, but with good reason. Cheap
shower pumps rely heavily on plastics in their construction.
Whilst there is nothing wrong with plastics technology it
happens to be a fact that pumps made mainly from plastic
don't last as long as their more expensive counterparts.
Pumps considered to be 'top end' products tend to be
constructed from metal - especially the impellor housings
that are often made of brass. It can often be a false
economy to buy a cheap pump as the brass-bodied models can
outlast them several times over.
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A noisy pump can
annoy you or drive you to despair! Pumps produce vibrations.
This is a fact that cannot be ignored or negated. If you are
looking for a vibration-free silent booster pump don't waste
your time. Some pumps will vibrate more than others. You can
probably guess that cheap pumps utilising cheaper materials
and made with less refined manufacturing techniques are
likely to vibrate more than their more expensive cousins.
As mentioned, vibration is the
culprit. Quality materials and accurately machined
components will minimise vibration and therefore noise
output but will not get rid of it entirely. It is important
to consider the transmission of vibration which is where the
noise comes from.
Manufacturers of the more
expensive brands of pump recognise this as a major issue.
Pumps are therefore made from quality materials such a
brass, motors are often of the 'induction type' that run
more quietly and the foot upon which the pump stands is
designed to absorb vibration - minimising transmission into
the surrounding area.
Apart from all the operational reasons that will
determine the most appropriate location for your pump, there
is the issue of vibration. Even the quietest most expensive
pumps will vibrate when in operation. It is therefore of
paramount importance that you consider well how and where to
put your little noise generator.
Place a shower booster pump
directly on a timber floor and you might as well stand it on
the sound box of a guitar. By it's hollow nature the guitar
sound box amplifies small vibrations from the strings so you
can hear them (by contrast a solid bodied electric guitar
needs an amplifier or it can't be heard). A hollow wooden
floor behaves in exactly the same way - amplifying
vibrations. Don't do it - the noise could drive you crazy!
Whenever possible you should
choose a location and/or stand your pump on materials where
transmission of vibration is minimised. A small pad stone,
maybe some sort of sandwich including rubber or polystyrene
leaves might be considered a suitable way to insulate
yourself from vibrations. Experiment but make sure the pump
will be secure.
Don't be surprised if having
ignored this advice you experience problems.
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Think in terms of where in
your system you intend to install your booster pump. Plan
things out before committing yourself to pipework. Never
forget that anything connected to the outboard side (the
boosted side) of the pump will cause the pump to activate
when used. To illustrate this point here follows an example
of how you may prefer not to do things...
A typical household decide to
up the performance of their gravity fed shower, so install a
3 bar shower booster pump next to the hot water cylinder in
the airing cupboard. Having done so, their shower became
quite a beast and gave an exhilarating experience to all who
used it.
One night the lady of the
house was awoken in the small hours by a thunderous noise.
She jumped out of bed in a panic to find out what on earth
the racket could be. She was surprised to bump into her
young daughter who was returning to her bedroom having been
to the toilet. "What on earth has happened?" asked the mum.
The daughter replied "I don't know, I've just been to the
toilet and flushed it." Upon investigation it transpired
that the plumber had fitted the twin impellor shower pump in
such a position that all water feeds to their bathroom were
now boosted. As the daughter flushed the toilet it activated
the booster pump. What was worse, the pump had been
positioned on the hollow floor in the airing cupboard which,
in the dead of night, sounded like a steam train thundering
through the house. It was subsequently discovered that not
only the shower and toilet been boosted, so too had the bath
and the wash basin. So, open a tap and the pump came on!
This story is absolutely true.
It highlights the very real considerations of installing a
pump and where you should insert it in your plumbing system.
If you only wish to boost the shower then make sure that's
all that is connected to the output of the pump. (Remember
to site it on something quite too!)
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