And which is best for my application?
Here at Arrow Valves we design and manufacture a wide range of Booster Sets for a variety of uses, from drinking water applications to Fluid Category 5 units for preventing contamination. The smaller Booster Sets have a single pump, which will be either Fixed or Variable Speed, and the larger units will have two pumps.
These larger Dual Pump units use Variable Speed pumps and are classed as either ‘Duty Standby’ or ‘Duty Assist’ – but what do these terms mean and what are the key differences between them?
First of all, lets look at the ‘Duty Standby’ pump arrangement. Only one pump ever runs at a time, the second pump is there to provide a backup if the first pump was to fail. The duty provided by the unit always remains the same, as the two pumps are identical.
A ‘Duty Standby’ configuration is used for critical applications, such as supplying equipment in a Hospital, where a backup pump would be needed to provide the full duty immediately if the first pump was to go into fault for any reason.
To ensure both pumps are evenly used, and to prevent stagnation or potential seizure, the lead pump is alternated on a daily basis. If the lead pump goes into fault, the second pump automatically takes over.
There is also a manual override switch “hand” located on the unit’s control box, which should be set to ‘Auto’ under normal operation. The switch allows either of the pumps to be manually isolated if required, ensuring only the healthy pump runs.
Now let’s look at the ‘Duty Assist’ pump arrangement. The main difference between this and the ‘Duty Standby’ configuration is that both of the pumps can run at the same time if needed.
Under normal operation only one small pump will run to meet the water demand. If the demand increases, the second small pump will automatically switch on. Using this type of arrangement offers substantial energy saving compared to one larger pump, and is also much quieter.
A ‘Duty Assist’ configuration is suited to applications where the demand is likely to vary a lot. For example, supplying a number of flats which will have a high demand at peak times in the day (early morning or evening when residents are more likely to have a shower or cook), but will have much lower demand at other periods throughout the day.
As with the ‘Duty Standby’ arrangement, the lead pump is alternated every twenty-four hours to ensure even usage. It is worth noting that if one of the pumps was to fail, the ‘Duty Assist’ Booster Set would be limited to half of its maximum flow rate, as only one of the small pumps would be operational.
Essentially there are pros and cons for both options. If you are unsure on which solution is best suited to your application, then please contact us to discuss the requirements of your project.
To summarise…
‘Duty Standby’ – only one pump runs at a time, if one pump fails the Booster Set can still supply the maximum duty.
‘Duty Assist’ – both pumps can run at the same time if required, more economical as smaller pumps can be used.
If you need any further information on this topic, or any other technical help, please feel free to give the Arrow Valves office a call or send us a message with any questions you may have.
