Pressure: Water pumps and accumulators

[atoll]

i would argue the need for an accumulator tank in small systems like you have in small yachts up to 60 ft,as all hot water calorifiers these days come with an over pressurisation relief valve,and there is enough expantion in the pipework any way,coupled with very sensitive pressure sensors on the pumps.
if the system is cycaling it means you either have a pump that is allowing backflow,a leak,or a tap that is not closed properly.

in very big systems yes definitly fit a large accumulater where there are many meters of pipe work and multiple bathrooms,but on your average 40 ft yacht it is not really needed with modern pumps.

[Suijin]

Originally Posted by Dave Lochner

We did the same this year. The pump works fine, quieter than the old pump and it doesn't go on in the middle of the night with the pressure dropped.



The Shurflo pumps say they can only prime from 6 ft. Not sure if that is vertical or horizontal fleet.

Same deal here. Three years ago my pump died. Replaced with 3.5 gpm Sureflo, ripped out the accumulator (yay reclaimed space, less complexity) and it's been great.

Noise from the pump can be dramatically attenuated through intelligent mounting. Mine is on grommets screwed to a board that is in turn mounted with neoprene backing. At normal flow it's little more than a hum.

Prime must be vertical as mine is more than 12' from the tanks' maybe a foot above and no problems self priming.

[deblen]

An explanation of how a domestic water system works. The only difference on a boat is the type of pump used.

https://www.youtube.com/watch?v=592Aw_ExaaY

[james247]

Originally Posted by Suijin

Same deal here. Three years ago my pump died. Replaced with 3.5 gpm Sureflo, ripped out the accumulator (yay reclaimed space, less complexity) and it's been great.

Noise from the pump can be dramatically attenuated through intelligent mounting. Mine is on grommets screwed to a board that is in turn mounted with neoprene backing. At normal flow it's little more than a hum.

Prime must be vertical as mine is more than 12' from the tanks' maybe a foot above and no problems self priming.

One of the major benefits of an accumulator is that it evens the pressure in the system. Stopping the hammering effect when the
Pump comes on. This hammering will cause joints to leak over time. An accumulator is not essential but it has a number of advantages.

5 bars of pressure is more than is needed on a yacht 3 should be plenty. In high rise buildings 2.5 to 4 is considered the norm.

The fact that it can accommodate additional pressure doesn't mean it's meant to be continuously at that pressure. It is engineering redundancy.

[atoll]

Originally Posted by deblen

An explanation of how a domestic water system works. The only difference on a boat is the type of pump used.

errr no that is possibly the worst example of a domestic water system in use ,totally reliant on electrical power etc

domestic systems world wide generally rely on gravity fed systems with header tanks fed by persurised municiple water that keeps the tank topped up,or direct in to the water system,no tanks or pumps needed
.
i have never seen a pressurised water tank on a yacht,the only case of that i saw was when someone tried to fill his tank with the vent closed with integral tanks and the tank exploded.

[Lepke]

The main purpose of an accumulator tank is to reduce the number of times your pump has to come on. It adds years to the life of the contacts and motor. Unless you have a house sized water heater, the expansion probably isn't enough to damage your plumbing.
Accumulator tanks are also used in hydronic heating to allow for the expansion of the water. Depending on the size of the system it maybe necessary. It also helps water hammer.

[FlightPlan]

Originally Posted by Lepke

The main purpose of an accumulator tank is to reduce the number of times your pump has to come on. It adds years to the life of the contacts and motor. Unless you have a house sized water heater, the expansion probably isn't enough to damage your plumbing.
Accumulator tanks are also used in hydronic heating to allow for the expansion of the water. Depending on the size of the system it maybe necessary. It also helps water hammer.

This is correct. No need for expansion tanks on a domestic hot water system anywhere. The HW tank has a temperature regulator and is sized to handle expansion. The usual pressure relief valve protects the tank from rupture if the temperature regulator fails, or inlet pressure of the domestic water system is greater than the tank design pressure.

The accumulator tank is good to have for the pressure water system to keep a constant pressure serving the fixtures. A pressure switch should be used when the system pressure reaches the required pressure, usually 40 to 50 psig. A check valve should be installed on the downstream side at the pump. It will keep pressure leaking back to the tank. The accumulator pressure should be charged at the tank with a bicycle pump to roughly 2 psig under the pump maximum dead head pressure.

Running the system without an accumulator will shorten the life of the pump, and or cause the pump to temporarily fail on thermal overload of the breaker.

[desdestiny]

Very interesting discussion.
I am an engineer and worked with pumps for 40 years. I had a new Variable speed pump on a new boat which died after 4 months. I pulled it apart to find out why this variable flow pump had failed. The fault was in the low cost pressure sensor used to trigger the pcb.
The pump is designed and built to be non serviceable and replaced - it is not designed to be repaired.
So my company has developed a variable flow device which uses an industrial grade pressure sensor, a PWM controller for motor voltage, and the pressure is adjustable with a potentiometer.

With manual systems with accumulator - the pressure in the system fluctuates between the high and low pressure settings. This creates variation in the flow and is annoying when having a shower. Also because of different flow paths through the hot and cold water lines, variation in pressure result in variations in water temperature under the shower. EVEN FLOW holds a constant pressure to avoid these problems.

The EVEN FLOW is controlled by a microprocessor - and we have built in many "intelligent" features
- low voltage shutdown - does not drain the battery.
- if a slow leak occurs in the system - the switch ON pressure is reduced to allow a very long delay before the pump turns back on.
- if there is a fault in the pressure sensor - an alarm light turns on

The EVEN FLOW pressure controller is designed as an aftermarket installation - it does not matter what pump it controls - it simply regulates the motor speed to hold constant pressure. All elements of the EVEN FLOW are repairable/replaceable.
See

https://www.youtube.com/watch?v=z96FgUBhzNQ

to see it working and switching between mechanical pressure switch and electronic control.

The accumulator is not needed and is best removed from the system.
Modern boating systems use plastic pipework which act as a pressure accumulator.
The hot water tank has a pressure relief valve to relieve pressure when the tank heats up.
email me for further information des@edgetec.net
http://www.cruisersforum.com/forums/...lies/smile.gif

[Dougtiff]

Hot water does NOT accumulate in the accumulator tank, the tank is filled from the water source, i.e., your on board tankage or city water, which ever you are using, 45 PSI, the normal presser used with a onboard pump is quite adequate, any higher, say 60 PSI, can become a issue with the fitting,i.e., hose clamps, if you have the PVC system's, like whale or Shark, you should be fine.

[Mike Banks]

Lived aboard for five years continuously and another three weekends. I replaced my water pump not long after coming aboard--and the electronic switch one with which I replaced the old one ran trouble-free without an accumulator all of that time--all I ever did was to replace the shitty bearings the pump came with with some decent ones--cost of twenty bucks--after about six years not because the pump failed but because it was noisy. Once the bearings were fixed using ones it should have had at the outset but for some bean-counter, it ran quietly for the rest of the time I used it.

The electronic ones work better without an accumulator--those with the old diaphragm and micro-switch type always run better with an accumulator. The electronic pump was a Jabsco par max 4., puts out 4.3 gallons per minute at about 50psi. They do make one that does a little more delivery per minute--but mine worked quite well.

[BruceS]

In answer to pressure to have in the accumulator ....
In my motorhome I carry a pushbike pump that has an adapter that will screw onto a car or truck valve & by turning on a cold water tap a weeny bit until the pump goes on/off/on/off I gradually pump up the pressure until I get the longest cycle time. If you go too much it shortens again .... just let a tiny bit out again.
Yes, there are now pumps that don't require them but they go all the time the tap is open. They use a LOT more power though.

[Kerry1]

Originally Posted by AndyEss

Talk about good timing - I'm working on my plumbing system this morning, and re-charging my accumulators/pressure tanks.
For pressurized water systems, the accumulator is more than just an expansion tank for the hot water heater to accomodate the expansion of water when it is heated.
The accumulator acts the same way as a large capacitor in a DC electrical system - it dampens out voltage (pressure) variations. Diaphragm pumps (Jabsco) as are most commonly used for boat/RV water systems put out a pulsating flow of water. The accumulator smoothens out the pressure pulsations. Further, the accumulator provides small volumes of pressurized water allowing the pump to cycle less. Fewer on/off cycles = longer pump life. Finally, if you hear the annoying sound of your pressure pump turining on at night when no one is using any water, it's the system re-pressurizing as pressure is lost through backflow within the pressure pump itself. The accumulator will greatly decrease the number of times this happens. Of course, this all depends on the size of the accumulator. The bigger the better in this case.
The bicycle (Schrader) valve on most tanks is to recharge the compressible element in the tank - air.
Most modern tanks have a membrane that separates the pressurized water from the air charge. You can check the pressure with a tire gauge. Older tanks have no membrane and depend on air that was entrapped in the tank when it was first filled up. Since air is fairly soluble in water, eventually this charge air disappears. These tanks have to be recharged occasionally.
Charge the tanks to a pressure somewhere below the hi-pressure cuttoff and the low pressure cut-in. I charge to 5 psi below the hi-pressure cutoff.

Excellent description of an accumulator's purpose.

[waterman46]

A little off topic, but in this thread some have mentioned it is desireable to reduce waterpump noise. Not so IMHO. Pump noise let's me know if I have run out of water and need to switch tanks, or if a tap has been left a little open, and if there should be a leak in the system.

[ranger58sb]

Originally Posted by canyonbat

Since we are on the subject, our accumulator has an air pressure fitting at the top. Any idea what pressure to fill the bladder?

Probably depends on the product, and manufacturer recommendations... and the pump it's paired with.

Our accumulator (Jabsco 30573-0000) comes pre-charged at 10 psi and that's the recommended air pressure. (Have to un-pressurize the water system to measure.)

YMMV, and you can probably get the manual from the maker's website... and you can probably use cut-in/cut-off info from the pump to further customize.

-Chris

[Dave22q]

If you have no insufficient pressure issues now, moving to a higher pressure pump makes no sense. More is not always better. Rather than swap out a pump that seems to have no problems beyond age, buy a cheap backup pump to protect against a sudden failure. Better yet, if you are generally within a day or two of port, install a manual backup galley pump or carry a 6g jug of fresh water.