Power fluctuations - electric supply

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laser
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Re: Power fluctuations - electric supply

Post by laser » Mon Jun 05, 2017 6:06 pm

This is a hydrofore type system that provides water with 14-18 m head (1.4-1.8 bar) at factory settings. The pump is controlled (on/off intermittent mode) trough a small pressurised 'vessel' (a bladder) and a pressure switch to prevent too frequent pumps starts and ensure relatively stable pressure. 'Constant pressure' is an exaggeration and bending the truth but for many purposes can fit the bill. Say, a change of discharge head from 18 m to 14 meter reduces the discharge by just slightly over 10%.

Right, let's sort this out. The symptoms and the successful remediation by the OP indicate a somewhat excessive pressure at the shower heater. There might be, but I cannot see other technically meaningful causes from the given info. Opening another tap increases the pump flow that in turn reduces the available head at the heater, which then magically works fine.

Fine, but I wanted to get some insight into, and 'feel' the numbers, the hydraulics. Made some assumptions about an average system like lengths of delivery pipes in series lengths, fitting numbers for estimating local losses, water temperature, elevations and then calculated the head losses for several operational conditions. Like when only the heater is on, an extra tap is open, and all taps are open. Those calculations are quite accurate but based on assumed data, and for that reason, can be quite off for some places, and pretty close for others. However, the resulting differences - that gave the change of head at the heater inlet - were consistent and revealing, and were not sensitive to changed input data. The results suggests that around 2 m head reduction could occur, which temporarily but consistently fixes the problem.

Instead of opening another tap during showers, the simplest solution might be a magic touch, slightly throttle the pump with the discharge side isolating valve (very likely a globe valve). Globe valves aren't made for flow control but can do the job. Their resistance is small until getting nearly closed. Therefore, first close the valve then open it by say 45 degrees), check the shower kick, and also open another tap to see the new, reduced flow rate. Repeat the procedure with small increases until satisfied. It makes no difference to the pump where and how the discharge pressure is 'used up' and won't do any harm.

Another option is to adjust the pressure switch, if that's possible with your pump model. Keeping in mind that 240 V is dangerous, find the pressure switch (just trace the cabling), which is normally protected/covered with a cup or similar enclosure to keep out condensation, dirt, and bugs. The adjustment involves turning a screw that changes the tension of a spring of the switch. There might be + - signs to indicate increased spring tension and pressure, and the reverse. It's a trial and error process, check the effect of adjustment on the shower. A good good idea is to mark the factory position of the screw, and while there clean the electrical contacts (not with WD-40).

Motor rev control is not working with traditional hydrofores but offers an alternative solution... for a price.
https://www.jaycar.com.au/speed-control ... s/p/KC5509

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Re: Power fluctuations - electric supply

Post by Nereus » Tue Jun 06, 2017 11:20 am

Hmm. It’s a water pump, not an engine from the space shuttle!

Not sure just what a hydrofore type system, but I guess that you mean Hydrophore.

By definition, a hydrophore system consists of a pump suppling a storage tank that accumulates a volume of water under pressure. The Mitsubishi unit posted by Geko, and what I at first thought was being discussed, is such a system. The system operates as I have posted and provides a reasonable linear pressure, but more importantly, a drawdown of several liters of water before the pump runs to restore the pressure. Larger size systems, such as used on ships and in hotels, use a separate accumulator tank with a much bigger volume, and therefore a much bigger drawdown before the pump has to run to restore the balance.

The Hitachi pump WM-P150XS is most definitely a “constant pressure” type of pump. The accumulator device containing the pressurized bladder is not much bigger than a bottle of water, and is NOT designed to provide for any drawdown of water. It is merely there to provide a sensing device for the pump pressure switch. Open a tap on the system and about a cupful of water will be drawn off before the pump kicks in and runs, and continues to run, while there is demand for water. If the flow of water from an open tap anywhere on the system is less than the output flow of the pump, then it COULD lead to “surging” as the OP has complained about. The pump will rapidly cut in and out as the pressure in the system builds up and then drops again.

Both systems are illustrated in the graphic link that I posted.
laser wrote:The symptoms and the successful remediation by the OP indicate a somewhat excessive pressure at the shower heater. There might be, but I cannot see other technically meaningful causes from the given info. Opening another tap increases the pump flow that in turn reduces the available head at the heater, which then magically works fine.
The flow from the pump CANNOT be increased, it is set by design. What does change is the pressure, which you may be referring to. Please refer to what the OP has posted.
The Shower Heater requires a constant and consistent flow of water in order for it to heat water properly and what is happening is the water flow to the Shower Heater is surging and not consistent when the tap/faucet is opened slightly and if the tap/faucet is fully opened then the water flow is too high and the water is cold.
What has been completely overlooked here is the shower heater. It also uses a “differential” type of device to sense the water flow to turn on the heaters. The device works on pressure differential, NOT flow. There has to be a drop of pressure across the sensing device for it to operate. As posted by the OP when the shower valve is only partly open the heater works fine. He wrongly assumes that with the shower valve fully open the flow is too high. It is not the flow, but the pressure is now too low to operate the heater switch. The pump is now happy because the flow is sufficient to keep the pressure below the cut-out point and it runs as a “constant pressure pump” as advertised.

The operating spec for the heater should show what supply pressure is required to operate the heater switch.

As a matter of interest, it is very difficult to calculate the total head against the pump. Many variables include the size and type of pipe, the number and type of fittings installed being just two of them. One ½” elbow is equal to around 3.5 feet of head; one tee piece is around 4.0 feet.

If you really want to work it out the following stolen from the Internet:

The "Darcy, Weisbach" tables are based on the head loss in clean, new pipe. The formula is:

HL = (F) X (L/D) X (V2/2g)

HL = Total Head Loss
F = Friction factor related to the roughness inside the pipe
L = Length of the pipe
D = Diameter of the pipe
V = Average liquid velocity in the pipe
2g = Two times the Universal Gravitation Constant (g=32.2 ft/sec)


There are several other “methods”, but one not often mentioned is “experience”!

In summary, the problem here is NOT the pump and it is NOT the water heater. It is simply a matter of the two not being suitable for use with the other!

For me the pump with only a 150 watt motor is only designed to supply 1 or 2 open taps or something like a toilet tank, where there is very little back pressure or restriction, in the system.
May you be in heaven half an hour before the devil know`s you`re dead!

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Re: Power fluctuations - electric supply

Post by Geko » Tue Jun 06, 2017 3:27 pm

I agree Nereus It’s a water pump, not an engine from the space shuttle!

Lets look at the pump specification on the brochure provided on several links on this thread:

The WM-P150XS has a designed capacity of 37 (Max 50) L/min.
Total discharge head pressure of: 13(M)
The brochure estimates a normal tap will flow at 8 L/min and that the pump will be able to supply 4-5 taps similaneously so should be ok for the job as 'Name Taken' only has 3 taps and a shower a water heater could have gone for a bigger pump but the largest on supports 6-7 taps simultaneously.

My money is still on a depleted accumulator, they are not designed for recharging in fact the manual stipulates do not remove the charging cap, plus you'd need adapters, gauges, nitrogen etc.

A new accumulator is about Baht 1700 on Lazada.

'Name Taken' you could always try borrowing an accumulator from a friends pump if the same to check out your system.

Take off the accumulator from your pump, empty water out of it re-install, and see if the problem is resolved (if ok you still need to buy a new accumulator)

Sorry for typo written in a hurry

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Re: Power fluctuations - electric supply

Post by NOKYAI » Tue Jun 06, 2017 4:27 pm

I have an old Hitachi water pump (broken shaft) in my pool house. Your welcome to come and rob bits off it if it would help!
Now semi retired 60:40 Thailand: UK ( seems to be working well)

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Re: Power fluctuations - electric supply

Post by NOKYAI » Tue Jun 06, 2017 4:35 pm

WM -P 250 GX if any of the parts are the same
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Re: Power fluctuations - electric supply

Post by Geko » Wed Jun 14, 2017 3:07 pm

Name Taken

Did you sort you water issue out?

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Re: Power fluctuations - electric supply

Post by Name Taken » Wed Jun 14, 2017 5:32 pm

Geko wrote:
Wed Jun 14, 2017 3:07 pm
Name Taken

Did you sort you water issue out?
Not Yet. :-|

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