Australian Water Management Review Vol 1 2010 | Página 60

Hydro
Innovations

How John Dee of Warwick saved on
capital costs and running costs by
using a new and innovative piping
design and pumps from Gorman-Rupp.

The Application
John Dee Warwick is a beef processor
(Abattoir) located in South East
Queensland. They wanted to upgrade their
waste water pumping system to enable
them to handle the day-to-day waste
water flows from their plant (estimated
to be 25 to 35 litres per second (l/s)),
but then to be able to ramp up to meet
additional flow demands during storm
conditions (estimated to be at least 60 l/s).
The static head in the system is only 3
metres, with discharged effluent running
through 450m of 150mm PVC piping.
John Dee wanted to use self priming
pumps to minimise their occupational
health and safety issues and to
minimise service costs over the life of
the installation.

at 1550 rpm with a 45kW electric motor to
deliver 61 l/s in the system.

The Options

Pros and Cons

The following options were considered for
the application:a.

A smaller pump to handle “day-today” flows, with the second pump
being a larger one to handle higher
“storm condition” flows.

b.

Two “medium sized” pumps to
operate alternately during normal
conditions, but both pumps
operating in series during the higher
flow demands.

Option A - One Small and One
Large Pump
It was ideal for John Dee to operate at
25 to 35 litres per second (l/s) during
normal operation. This perfectly suited
the Gorman-Rupp T4A3S-B Super T
Series Trash pump. It could operate at
1100 rpm with a 5.5kW electric motor to
deliver 25 l/s.
John Dee needed the second pump to
deliver at least 60 l/s, but wanted to
be able to pump at less than this flow
occasionally to cover some “peak” normal
conditions that the smaller pump was
not coping with. It was therefore ideal for
this pump to be controlled with a Variable
Frequency Drive (VFD). This duty suited
the Gorman-Rupp V6A60-B, which can run

Water Management Review 2010

Gorman-Rupp Parallel/Series pumping unit being installed. Note the interconnecting piping.

The main advantage of this system is its
flexibility with regard to flow rate. With
the VFD, operators can ramp the pump
speed up during higher flows and back
down during lower inflow periods. If John
Dee wanted to, they could opt for a larger
motor (75kW maximum), which would
then give them the capacity to ramp flow
up to 70 l/s even if piping was the higher
pressure rating.
The disadvantages of the system are as
follows:• The capital costs are much higher
because of the cost of the higher
performance pump, but mainly due to
the higher cost of the VFD controls.
If John Dee went for maximum
flexibility, this system would be the
most expensive by up to $30,000 (or
approximately 50% more) not including
what might be the added cost for
running power to a 75kW motor.
• There is no spare parts compatibility
between the pumps, so any
emergency parts stock the plant might
want to carry, would need to be for
two different pump models.
• Pumps would not wear evenly, and
the plant might find that their larger

pump is in “near new” condition in 5
years but the smaller pump needs an
upgrade because it’s been doing all
the work.

Option B - Two “Medium Sized
Pumps, with Parallel/Series Piping
This option uses 2 pumps (both GormanRupp T6A3S-B Super T Series), which are
set up to operate alternatively. The piping
is connected the same as a “normal”
duty/standby pumping arrangement
except for the addition of some minor
but critical interconnecting piping.
Instead of both pumps only being able to
pump into the common discharge line,
interconnecting piping is added along
with an additional non-return valve and an
additional isolation valve. Gorman-Rupp
call this “Parallel/Series Piping”. This
additional piping now allows the pumps
to operate as series connected pumps
when the second pump is called upon to
operate, while still allowing single pumps
to alternate.
When a single pump operates it will
produce 44 l/s. This is higher than the
target flow rate (25 to 35 l/s) for 1 pump,
but because pumps can alternate, there
are no problems for the motors in the
“starts per hour” area. This flow rate also
covers off that intermediate flow area that
the previous option needed to cover with
the large pump running slower through
the VFD.