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Water pump pressure question


Whitey62

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Hi all,

  my potable water pump has given up the ghost or at least I think it is about to!

  Sounding very noisy though the noise  has gradually increased over last 6 months so wasn’t really noticed.

  Pulling the battery voltage down after   10 seconds running and cuts out after about 30 seconds.

  It is a shurflo 20psi model.

  I am happy to replace with similar/same as the price suits me down to the ground but my question is can I go for a higher pressure pump without doing damage to water heater and would the higher pressure be of any actual benefit? 

  I have a Morco D-51b which has been fine up to now but I am about to spend my first winter as a live aboard and Would like a boost to shower pressure as long as it comes with enough hot water to make the pressure boost enjoyable.

  Thanks in advance for any and all advice and opinions    
   Paul 

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Be aware that increasing the cold water pressure will not boost the hot  shower pressure or give you more hot water at the same temperature.q.  This is a consequence of the way the water heater works.  You can have more water over your bod, but it has to be cooler water as the amount of heat put in by the Morco is fixed. 

 

When you replace your water pump, fit a separate adjustable pressure switch like a Square D.  They last a lot longer and you can tune the on and off pressures to suit your system.

 

N

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46 minutes ago, Whitey62 said:

Hi all,

  my potable water pump has given up the ghost or at least I think it is about to!

  Sounding very noisy though the noise  has gradually increased over last 6 months so wasn’t really noticed.

  Pulling the battery voltage down after   10 seconds running and cuts out after about 30 seconds.

  It is a shurflo 20psi model.

  I am happy to replace with similar/same as the price suits me down to the ground but my question is can I go for a higher pressure pump without doing damage to water heater and would the higher pressure be of any actual benefit? 

  I have a Morco D-51b which has been fine up to now but I am about to spend my first winter as a live aboard and Would like a boost to shower pressure as long as it comes with enough hot water to make the pressure boost enjoyable.

  Thanks in advance for any and all advice and opinions    
   Paul 

 

A bit of ambiguity here I feel. Does the pump cut out because the water pressure is high enough or does it cut out because the voltage is too low?

 

It is to expected that a water pump will pull the voltage down to a small degree but once pulled down it should stay the same until the pump cuts out. If it is pulling the voltage down at, or close to, the batterers by half a volt or more then something is wrong. I would initially suspect faulty or flat batteries.

 

The increasing noise could indicate a restriction in the water supply to the pump so check the strainer that should be on/in the inlet pipe, make sure any tank isolation valve is fully open and if its an old boat check any steel pipes on the tank outlet have not rusted up.

 

Note what BEngo said about the water temper tare and the way those heaters work. If the pump is cutting out on the pressure switch you ca probably boost the cut out pressure by adjusting the screw in the end of the pump but don't go higher than the pressure Morco give as a maximum and if you also have a calorifier don't go any higher than 5 to 10 psi below the PRV setting.

 

 

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8 minutes ago, Tony Brooks said:

 

A bit of ambiguity here I feel. Does the pump cut out because the water pressure is high enough or does it cut out because the voltage is too low?

 

It is to expected that a water pump will pull the voltage down to a small degree but once pulled down it should stay the same until the pump cuts out. If it is pulling the voltage down at, or close to, the batterers by half a volt or more then something is wrong. I would initially suspect faulty or flat batteries.

 

The increasing noise could indicate a restriction in the water supply to the pump so check the strainer that should be on/in the inlet pipe, make sure any tank isolation valve is fully open and if its an old boat check any steel pipes on the tank outlet have not rusted up.

 

Note what BEngo said about the water temper tare and the way those heaters work. If the pump is cutting out on the pressure switch you ca probably boost the cut out pressure by adjusting the screw in the end of the pump but don't go higher than the pressure Morco give as a maximum and if you also have a calorifier don't go any higher than 5 to 10 psi below the PRV setting.

 

 

I have tested out the battery bank and all is fine.

  Water supply is plastic and filter is clear.

  I do not have a calorifier, just a morco water heater.

  Voltage drops around .5 volts after 30 secs, pump is hot at this point and cuts out.

   I havent measured the drawn current as a I believed the hot pump was a clear indicator of being faulty, swollen diaphragms/seals I suspect? 
   I’ve just done a little research and it seems if I want higher shower pressure then I need more hot water which means I need a larger capacity water heater……….does that sound about right? 
   I’m thinking buy the 45psi pump and adjust pressure to suit current system then purchase a larger heater when funds allow and readjust pressure to suit.

  Does that sound about right or am I thinking too simply? 

  

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11 minutes ago, Whitey62 said:

I’ve just done a little research and it seems if I want higher shower pressure then I need more hot water which means I need a larger capacity water heater……….does that sound about right? 

Instantaneous water heaters like the Morco have a fixed heat output. So lower flow and hotter water or vice versa. So if you want more flow that you get at present without reducing the temperature, then you need a higher output heater, regardless of any pump issues.

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1 minute ago, David Mack said:

Instantaneous water heaters like the Morco have a fixed heat output. So lower flow and hotter water or vice versa. So if you want more flow that you get at present without reducing the temperature, then you need a higher output heater, regardless of any pump issues.

I get that now, thank you 

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Yes, bigger water heater potentially  equals hotter/greater flow shower.  And bigger gas bills.  You also may need a bigger gas regulator. You may even need bigger gas pipes if they are not already large enough.  Read the new q heater data carefully.

 The pressure you need will be determined by what the water heater needs as a minimum, and what it will stand as a maximum.  Expect these to be about 1 bar min and 3.5 bar max, but again, read the heater data very  carefully before buying.

 

If you tell us the max and min pressures needed we can advise on a suitable Square D pressure switch.

 

N

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3 minutes ago, David Mack said:

The D51B is rated at 8.7kW. Current equivalent models are more, so an upgrade is potentially possible. But note that higher output means more gas consumption, so your existing regulator and pipework may also need uprating.

Thanks David, it all makes sense when simply stated……appreciated

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11 minutes ago, Whitey62 said:

Thanks David, it all makes sense when simply stated……appreciated

 

If you need to increase your gas pipe size, and don't, then it will become obvious to the BSS examiner as when everything is lit, you won't have enough gas supply and will get a BSS fail, if the flame pattern is incorrect.

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I have a permanent pressure gauge on my water system which tells me a lot of interesting things (sad git).

The pump pressure is the pressure the system gets to with all the taps turned off, and is mostly controlled by the setting of the pressure switch in the pump.

With a tap open/water flowing the pressure drops to about 0.5bar. I assume this is controlled by the flow rate (not pressure) that the pump can deliver and the restriction of the pipes. So if you want more water flow or a higher working pressure I suspect getting a pump with more flow, not a higher pressure, is the way to go.

 

My gauge is on the calorifier which is a long way from the pump and taps so my figures might not be fully reliable, I need to experiment. 😀

 

 

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23 minutes ago, Alan de Enfield said:

 

If you need to increase your gas pipe size, and don't, then it will become obvious to the BSS examiner as when everything is lit, you won't have enough gas supply and will get a BSS fail, if the flame pattern is incorrect.

This is one of the (many ) anomalies of the BSS.  Nearly all gas burners are naturally aspirated, so, as you reduce the inlet pressure the flow of gas decreases  and the amount of air drawn in also reduces.  This means  that the flame picture does not change much, albeit the flame gets a bit smaller, until the pressure is very much too low.  This is an essential characteristic of gas cooker rings and  oven burners,à or all these devices would potentially be lethal at anything other than one setting.

 

The only way to check gas pressure properly is to put a pressure gauge (manometer) on the appliance inlet and see what actually happens at full load..  Most modern  gas appliances, except cookers,  have a buit in test point  so they can be properly commissioned. Using the test point constitutes gas work so it's outside the provenance of "ordinary" BSS examiners, leading to the unlikely to fail flame picture test.

 

N

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1 hour ago, Whitey62 said:

I have tested out the battery bank and all is fine.

  Water supply is plastic and filter is clear.

  I do not have a calorifier, just a morco water heater.

  Voltage drops around .5 volts after 30 secs, pump is hot at this point and cuts out.

   I havent measured the drawn current as a I believed the hot pump was a clear indicator of being faulty, swollen diaphragms/seals I suspect? 
   I’ve just done a little research and it seems if I want higher shower pressure then I need more hot water which means I need a larger capacity water heater……….does that sound about right? 
   I’m thinking buy the 45psi pump and adjust pressure to suit current system then purchase a larger heater when funds allow and readjust pressure to suit.

  Does that sound about right or am I thinking too simply? 

  

 

A hot pump could also be a symptom of undersized wirirng causing excess volt drop. That would cause the pump speed to drop and the current consumption to rise. Personally I would get  a length of cable so you can measure the voltage between the battery pos and the pump positive with the pump running. the meter should read no more than about 0.5 volt. Then the same between the two negative points. Expect the same voltage. Otherwise measure the voltage across the batteries  while the motor is running and then across the connections at the pump with it running and subtract to find the volt drop. you won't want to ruin a new pump because of insufficient operating voltage.

 

Is the supply pipe plastic all the way into the tank? Many tanks have a short length of steel take off pipe.

 

I have never hear of water pump diaphragms  or seals swelling, I have heard of seals failing so water gets into the motor and rusts it up

 

As for the pressure just be aware the higher the pressure the greater the chnace of plumbing leaks.

 

 

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