Water Pump and Accumulator query

[Michael Siggers]

Hi

 

Posted on here a while ago about my Bukh DV36 engine and will provide an update soon.

 

In the meantime......

 

So, today, I changed my Water Pump as it started to malfunction and not kick in when taps opened etc. The pump was a Jubasco Pur Max 3.5 which I soon found out was discontinued about 4 years ago. So, not a bad performance for the Pump. Anyway, I purchased a Jubasco Pur Max HD4 which has exactly the same Cut In and Cut Out pressure specifications, but a slightly higher flow rate.

 

As it is the same make as the old one, it was a straight swap and went more smoothly than I had anticipated, bar a little spilt Water.

 

All connected and powered up and is working well. Better Water flow at the taps too. With the old one, sometimes the taps would reduce to a mere dribble before the pump kicked in.

 

As the title suggests, I also have an accumulator although I have to guess at the capacity at 5 ish litres as the manufacturer has put everything one the label, including what they had for lunch, apart from the capacity. I'll admit, I do need to check the pressue is correct which is a job for tomorrow, as well as improving the support for the accumulator.

 

Anyway, when I switched the new Pump on, it operated and charged the accumulator, then shut off. Turn the tap on, water flows and then the pump kicks in a little while later once the accumulator has run out of steam. Turn the tap of, pump continues to run for 5 - 10 seconds, recharging the accumulator.

 

Therefore, all seems to be working OK.

 

The query I have relates to the operation that should happen if I leave a tap on for a long time. Not a usual habit, but I guess more applicable to when I run the shower. Never thought about it before, but am I correct in thinking that the pump will/should run continuously while the tap is open/shower running, only turning off after the tap/shower is closed and the accumulator recharged. In other words, it's not supposed to start and stop at various intervals during the open tap/shower while it recharges the accumulator mid flow? Hope that last bit makes sense.

 

Kind regards

 

Mike

[ditchcrawler]

When I turn the shower on the water flows for a short time then the pump starts, The pump is of large enough capacity to both supply the shower and recharge the accumulator, at that point the pump cuts out until the pressure falls low enough for the pump to cut in again.

[Michael Siggers]

12 minutes ago, ditchcrawler said:

When I turn the shower on the water flows for a short time then the pump starts, The pump is of large enough capacity to both supply the shower and recharge the accumulator, at that point the pump cuts out until the pressure falls low enough for the pump to cut in again.

Thank you

 

So your pump does not run continously while the shower is running?

 

Mike

[blackrose]

Until you've checked the pressure of the accumulator (with the pump switched off and taps open) and made sure it's correct in relation to the new pump pressure,  there's no real point asking if the pump is behaving how it's supposed to.

Accumulator tanks should be set at or a couple of psi BELOW the water pump's CUT-IN pressure.

 

If you have a hot water expansion vessel in the system it's worth checking that at the same time. HW expansion vessels should be set at or a couple of psi ABOVE the pump CUT OUT pressure, again with pump switched off and a couple of taps open.

Edited February 20 by blackrose

[Tony Brooks]

9 hours ago, Michael Siggers said:

The query I have relates to the operation that should happen if I leave a tap on for a long time. Not a usual habit, but I guess more applicable to when I run the shower. Never thought about it before, but am I correct in thinking that the pump will/should run continuously while the tap is open/shower running, only turning off after the tap/shower is closed and the accumulator recharged. In other words, it's not supposed to start and stop at various intervals during the open tap/shower while it recharges the accumulator mid flow? Hope that last bit makes sense.

 

The answer depends upon the pump output volume and the volume flowing from the shower or the tap(s). If the potential flow rate from the outlet is the same or greater than the pump output, then the pump will run all the time the outlet is open. If the outlet flow is less than the pump output, then the pump will cycle.

[Iain_S]

17 hours ago, Michael Siggers said:

(snip)

The query I have relates to the operation that should happen if I leave a tap on for a long time. Not a usual habit, but I guess more applicable to when I run the shower. Never thought about it before, but am I correct in thinking that the pump will/should run continuously while the tap is open/shower running, only turning off after the tap/shower is closed and the accumulator recharged. In other words, it's not supposed to start and stop at various intervals during the open tap/shower while it recharges the accumulator mid flow? Hope that last bit makes sense.

 

Kind regards

 

Mike

As others have said, quite normal for the pump to cut in and out when tap  open continuously, depending on flow rate.

With a shower, depending on the source of hot water, it may smooth out temperature variations if there is an additional cold tap running enough to make the pump run without cutting out/in. Effect particularly marked  if hot water comes from an instant water heater.

[Michael Siggers]

7 minutes ago, Iain_S said:

quite normal for the pump to cut in and out when tap  open continuously

Just to clarify.......

 

With the COLD tap open FULLY, the pump should run all the time, as there is no chance for the Accumulator to be recharged, as the water is constantly flowing. How would the Accumulator recharge if there is constant demand from the COLD Tap, once the pre-charged accumulator has run out after the initial turn on?

[Tony Brooks]

5 minutes ago, Michael Siggers said:

Just to clarify.......

 

With the COLD tap open FULLY, the pump should run all the time, as there is no chance for the Accumulator to be recharged, as the water is constantly flowing. How would the Accumulator recharge if there is constant demand from the COLD Tap, once the pre-charged accumulator has run out after the initial turn on?

 

As I explained, if the tap output is less than the pump output. The difference between the two outputs increases the system pressure until it is sufficient for the pump to cut out. Then, unless you close the tap, the system pressure will drop until the pump cuts back in.

 

Have you actually measured the output from the tap? There will also be some resistance to flow through the pipes and fittings that will further reduce the flow from the tap, but it won't be that much with15mm pipe so we may as well ignore it for a boat.

 

Whether the pup cycles or not with an outlet open solely depends on the input (pump) and output (tap) flow rates. The accumulator can only alter the on-off ratio of any cycling, bu it can't stop it if less is flowing out than the pump is putting in.

Edited February 20 by Tony Brooks