GT40s.com
MK-I  MK-II  MK-III  MK-IV  GULF  MIRAGE  J-CAR  LOLA
GT40s.com
Home Forum Gallery Support GT40s.com  
Register FAQ Advertisers Search Today's Posts Mark Forums Read

Go Back   GT40s.com > Non-Motorhead Discussion > The Paddock


The Paddock Enter at your own risk.

Reply
 
LinkBack Thread Tools Display Modes
Old 16th November 2004, 04:50 AM   #1 (permalink)
Malcolm's Avatar
Malcolm
Gold Supporter
United Kingdom
 
Join Date: Jun 2003
Location: Surrey, UK
GT40: GTD
Posts: 2,346
Hydraulic engineering advice needed!

I have very high water pressure in the house. I have it reduced to 3 bar at the mains in point. Every tap (hot and cold) is at full mains pressure. These are fixed paramteres.

My shower head keeps exploding (blows its gasket) sending water across the bath room in to the light fittings. I am not changing the shower head (8 inch diameter pan) but want to drill out each hole to reduce pressure. I already have a reducer in the supply pipe reducing it from 15 mm to 3mm!

Question. To reduce the water back pressure in the shower head by 50% is it a matter of just increasing the area of each hole by 100% ie double the water outlets area?

I only want to drill this shower head once!
Malcolm is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 06:23 AM   #2 (permalink)
wbmusarra's Avatar
wbmusarra
I Have No Life
United States
 
Join Date: Oct 2001
Location: Snellville, Ga.
GT40: DRB#5
Posts: 2,742
Re: Hydraulic engineering advice needed!

Malcom,
Since you are metric, I'll explain what I have had the experience in english measurements. My outwide pressure is >150 # pressure. There should be a pressure reducing valve inside the house on the main feed line that should reduce the pressure to about 50 to 70#. It is adjustable, but most are preset at the factoy). As the water is heated, the pressure in the system will rise due to expansion. What you need is:
1.A "potable water expansion tank". It is basicly a tank that has a rubber bladder and is divided in two chambers. As the water expands the air tank absorbs the pressure. Most have an air valve as on a bicycle so as the pressure can be adjusted.
2. On the low side of your house(someplace where the line is accesable and on an outside wall preferrably near an outside faucet) you need to install an adjustable pop off valve with the exit outside of the house. Set it it 125# or so. That way if the pressure gets above it, the excess will be vented outside of the house(You will see it dripping if the pressure is above that).
The pressure you are talking about is way too high and will eventually burst a pipe somewhere else in your house causing more than the damage you describe. You nee to do this right away.
Hope this helps.
Bill
wbmusarra is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 06:46 AM   #3 (permalink)
Malcolm's Avatar
Malcolm
Gold Supporter
United Kingdom
 
Join Date: Jun 2003
Location: Surrey, UK
GT40: GTD
Posts: 2,346
Re: Hydraulic engineering advice needed!

Thanks for the thoughts Bill, but don't agree with your conclusion! My system is a pressurised system with expansion bladders etc built in already. UK ratings for equipement typically cope with 3 bar as the standard. My inlet pressure was 5 bar (70 psi) and that is too much so it was reduced at the mains water in point as mentioned. Maybe the UK/USA language barrier has kicked in as I do not know what # means as a unit.

The shower unit used is not an environmentally friendly one. It can shift 15 gallons a minute! Having a deep bath uses less water than a 5 minute shower.

My thoughts are that the seal on the shower head is just over its operational tolerances. Hence it fails as the weak link in the system. I wish to reduce the work it has to do by releiving its work load. Letting the water out of the shower head more quickly by increasing the jet hole sizes should do this. Clearly this could be done by trial and error but I thought I woukld see if there was known a mathematical engineering way first. There has to be but who knows it?

If this is a linear solution then as you increase hole size, pressure drops accordingly when volume remains static. But I suspect it isn't linear. Water temperature is fixed in this discussion as I have a stop on the theormostatic valve at 38 C which is before the shower head.

This has to be similar to air flow into your engine to exhaust gases flow out (but without all the complications of combustion)? Or venturi in aerodynamics?

Just a bit of fun. Shame Wendy's maths is terrible, otherwise I could encourage her into the shower with me to work this one out!!!!! Hey ho.

PS Is Bar a metric measuremnt? I think metric equvalent is Kn/m sq. Lets not go there. [img]/ubbthreads/images/graemlins/smile.gif[/img]
Malcolm is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 07:22 AM   #4 (permalink)
huntsen's Avatar
huntsen
8 Tenths
United Kingdom
 
Join Date: Oct 2003
Location: High Wycombe, U
GT40: Factory-blt GTD
Posts: 817
Re: Hydraulic engineering advice needed!

Malcolm,
1Bar is just under 1 atmosphere - ie about 14.7 pounds per square inch.
The hole size necessary to relieve the head pressure will depend on flow rate.
Think about it, no flow (blocked holes) and the full line pressure will appear at the head seal. If the holes are 'infinitely' big, the head seal will see next to no pressure. What you want is to increase the flow rate (even more!) such that the head seal sees just the right pressure.
Without knowing your existing flow rate it's a bit difficult to advise. I suggest increasing the holes size by a little bit and seeing what effect it has on pressure. Then you can judge whether it needs to be a lot more, a little bit more or just right.
huntsen is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 07:26 AM   #5 (permalink)
flatchat's Avatar
flatchat
Silver Supporter
Australia
 
Join Date: Dec 2002
Location: Warwick,Q 4370
GT40: RCR T70 spyder
Posts: 1,660
Re: Hydraulic engineering advice needed!

Elementry my son--It sounds like Wendy is the cause of your high water pressure [img]/ubbthreads/images/graemlins/grin.gif[/img]
hope your wife doesn't read this [img]/ubbthreads/images/graemlins/blush.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]
flatchat is online now  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 08:12 AM   #6 (permalink)
Chris Liokos's Avatar
Chris Liokos
7 Tenths
Australia
 
Join Date: Nov 2001
Location: Australia
GT40: RF40
Posts: 766
Re: Hydraulic engineering advice needed!

Malcolm,

Just some educated estimates here.

The pressure downstream of the shower regulator (in this case the tap valve) is determined by you. If you want less pressure at the shower head then just donít turn the tap up as much.

However, if for some reason you cannot regulate the water flow at the tap (maybe its just too hard trying to determine what point is too much) then the pressure in the shower head would not be determined by the size of the holes as such, unless you drill the holes such that the total area of all holes combined are greater than the total cross-sectional area of the pipe that feeds it. In short, if the water canít be expelled as fast as it can be fed, then the pressure will eventually reach near enough maximum at a point immediately before the shower head holes.

A better solution, I think, would be to put a fixed restrictor of some sort anywhere up-stream of the shower head. This restrictor should have the same (or less) cross-sectional area of all current shower-head holes combined. In that way, you will be reducing your water usage too.

Just one final point. My explanation does not take into account the momentum of the flowing water. If you have the tap turned up full and your water is flowing at a rate of a gazillion gallons per second, then the forces created by having to re-direct that water around a corner, down the head and around the holes will have consequences in itself. This however is not a water pressure issue, but a kinetic energy issue created by the movement of the water. Again, use the restrictor to solve this problem too.
Chris Liokos is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 12:37 PM   #7 (permalink)
Malcolm's Avatar
Malcolm
Gold Supporter
United Kingdom
 
Join Date: Jun 2003
Location: Surrey, UK
GT40: GTD
Posts: 2,346
Re: Hydraulic engineering advice needed!

Ha, you try and tell guests not to turn the shower on too much!

I do have a restrictor in the line just before the shower head. It is a 1/8 inch diameter hole (3mm) and still it blows the gasket!

But we seem to be getting soemwhere. I guess the area of the restrictor hole needs to be smaller than all the outlet holes combined to reduce pressure. I have 75 outlet holes (sad aren't I to count them) with each having a diameter or about 1/32 inch to 3/64 inch, when clear of scale! I can't measure accurately that small. But this totals much more than the area of a circle 1/8 inch diameter. Interestingly the water flow rate when in use having a shower, seems to be the same with or without the restrictor in place, so clearly the shower head is creating back pressure. Blows the gasket a lot quicker than without the restrictor though.

So as Tony says, I want to increase the flow rate by letting more water out the shower head over the same period of time. So back the to theoretical question posed at the start. If I drill out the shower head holes to twice their existing area ie double the outlet area in total but leaving the inlet area via the restrictor the same, will this halve the back pressure I am suffering from?
Malcolm is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 01:33 PM   #8 (permalink)
David Morton's Avatar
David Morton
Lifetime Premier Supporter
United Kingdom
 
Join Date: Nov 2002
Location: Marlow, England
GT40: The Jewel on th
Posts: 5,945
Re: Hydraulic engineering advice needed!

Run a seperate feed from your cold water tank to the shower and it willl only then be at Gravity fed P. Is the shower thermostatic?
David Morton is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 02:22 PM   #9 (permalink)
BenL's Avatar
BenL
9 Tenths
United States
 
Join Date: Apr 2004
Location: USA
Posts: 923
Re: Hydraulic engineering advice needed!

Bill's solution agrees with what I learned in the plumbing part of my home inspection class.

If the water pressure for your house is too high (more than 70PSI), you should install a pressure reducing valve at the point where the water line comes into the house (after the meter). You'll also need to install an expansion tank down stream of the pressure reducing valve because you can no longer use the water main in the street for expansion (water hammer).

As you've learned with your exploding shower head, household appliances (faucets, dish washers, washing machines, toilets, ...) are not designed for high pressures and frequently manufacturer warrantees have a clause saying that they don't cover failure because of high water pressure.

Drilling out the holes in the shower head might help with the exploding shower head problem, but I'd worry about the other appliances in your house.
BenL is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 06:55 PM   #10 (permalink)
David Morton's Avatar
David Morton
Lifetime Premier Supporter
United Kingdom
 
Join Date: Nov 2002
Location: Marlow, England
GT40: The Jewel on th
Posts: 5,945
Re: Hydraulic engineering advice needed!

Once again, run the seperate feed to that shower only and you will have a stable system. No need for flow restrictors, pressure reducing,valves, and if you can use 22mm all the way, though a lot of showers , including some power showers, are now using 15mm. If using a thermostatic cartridge, the cartridge will hunt less witout mains pressure which continually varies anyway. Is your boiler system a combi or an indirect? If you are using the combi type then Aqualisa do a shower CWP regulating system, but if you bite the bullet iand instal the pwer shower from them as well, it's and integral part of their pump.
PS I am not a plumber or affiliated to Aqualisa.
David Morton is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th November 2004, 10:45 PM   #11 (permalink)
patbarry's Avatar
Gold Supporter
United States
 
Join Date: Apr 2002
GT40: Houston, Texas
Posts: 649
Re: Hydraulic engineering advice needed!

YOu have an exploding shower head at 3 bar (which is 70 psi, your number)? That doesn't sound right. Where is all this pressure coming from? I do a lot of work in the water business, (granted, in the US, not UK), but I would imagine the systems are similar. 70 psi is high, but not too high, hell, that sounds good. I must not be understanding this correctly.
patbarry is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th November 2004, 04:53 AM   #12 (permalink)
Malcolm's Avatar
Malcolm
Gold Supporter
United Kingdom
 
Join Date: Jun 2003
Location: Surrey, UK
GT40: GTD
Posts: 2,346
Re: Hydraulic engineering advice needed!

Sorry guys but you all seem to be hanging onto an overly high pressure that doesn't exist! I have said my system is running at 3 bar after the water mains inlet pressure reducer from 5 to 3 bar. That is only about 45 psi. My system is a Heatrae Sadia Mega Flow system. It states its output for hot water is 3 bar so hot and cold are both at 3 bar. I have no cold water tank in the attic, everything is direct fed mains pressure. There are no problems with my water system. If you are installing a new plumbing system in your house, check out mega flows, I have used them many times now in all the houses I have built and I also use zero water storage tanks in my commercial property too. I have zero pumps on my shower. Power showers run at 1.5 bar. Use a mega flow tank system on a power shower and you will kill it.

I have a crappy shower head seal, but the shower head looks nice so I want to keep it as opposed to paying a fortune for a new properly sealing shower head that also looks nice. A drill costs way less than a new shower head.

FWIW the shower unit is a thermostatically controlled mixer unit that is fed by 22mm (3/4 inch) pipes but feeds the shower head in 15mm (1/2 inch'ish). This is typically standard.

So we are back to a crappy shower head and seal. Maybe I should have said that at the start! I am very tempted to now bring this shower head to the karting evening tomorrow for debate as I see names above who are coming!!!!!!
Malcolm is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th November 2004, 08:34 AM   #13 (permalink)
Chris Liokos's Avatar
Chris Liokos
7 Tenths
Australia
 
Join Date: Nov 2001
Location: Australia
GT40: RF40
Posts: 766
Re: Hydraulic engineering advice needed!

[ QUOTE ]
Blows the gasket a lot quicker than without the restrictor though.

[/ QUOTE ]

Malcolm,

This is much more fun for us who can play "theory" since we don't have to get wet and dirty (as the actress said to the bishop). [img]/ubbthreads/images/graemlins/grin.gif[/img]

However, I still maintain that the pressure is not regulated by the size of the shower-head holes if the restrictor is letting more water through than the head can expel. The best that you can hope for is that the pressure build-up at the shower head will be SLOWED, but EVENTUALLY if the shower lasts long enough the pressure at the head will equalize with the pressure before the restrictor and still end up blowing your seal, as you have discovered.

OK, thats the fun theory out of the way. Actually, I think that you just have a dud shower head.
Chris Liokos is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th November 2004, 10:11 AM   #14 (permalink)
Chris Liokos's Avatar
Chris Liokos
7 Tenths
Australia
 
Join Date: Nov 2001
Location: Australia
GT40: RF40
Posts: 766
Re: Hydraulic engineering advice needed!

Just reading back my comments, I'm not sure that I exactly answered your question. My main point was that there is not a gradual reduction in pressure as you change the shower-head hole-size, but a cross-over point at which point the high pressure will be reduced permanently.
Chris Liokos is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

 
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 06:02 PM.