Pressure in outdoor water tap is no good

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Discussion Overview

The discussion revolves around the perceived decrease in water pressure from an outdoor water valve after it was replaced. Participants explore the implications of valve and pipe sizes, as well as the relationship between pressure and flow rate in the context of garden hoses and outdoor water systems.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that the new valve has a longer pipe end and a diameter of Ø22 mm, questioning whether increasing the supply pipe size would improve pressure.
  • Another participant asks about the changes made between the two valves, suggesting that different types may affect performance.
  • A participant emphasizes the importance of ensuring both valves have similar Cv or Kv values to compare their performance accurately.
  • It is proposed that increasing the supply pipe size could help with pressure at the valve, but changing the valve might be simpler if the previous pressure was acceptable.
  • Some participants speculate that the old valve may have had a smaller supply pipe (15 mm), which could have delivered less water but with better pressure at the end.
  • One participant argues that larger piping and valves should provide lower resistance, leading to greater flow and pressure at the end, assuming the nozzle remains unchanged.
  • Another participant mentions that pinching the hose can increase perceived pressure, raising the question of whether reducing the supply pipe size could have a similar effect.
  • A participant clarifies the distinction between force and pressure, suggesting that to achieve greater pressure, the diameter of the valve should be changed.
  • Concerns are raised about the potential for increased loss in the system if the valve size is altered without considering the overall design.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between valve size, pipe size, and water pressure. There is no consensus on the best approach to resolve the issue, and multiple competing perspectives remain throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the specific configurations of the valves and hoses involved, as well as the implications of changing pipe sizes on pressure and flow. The discussion does not resolve these uncertainties.

Who May Find This Useful

This discussion may be of interest to individuals involved in plumbing, irrigation systems, or those seeking to understand the dynamics of water flow and pressure in outdoor applications.

TSN79
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My company delivered an outdoor water valve (the kind you connect your garden hose to). The guy called me the other day telling me that he thought the water now had less "force" coming out the end that it used to with his old valve. The valve has a 20cm long pipe end to connect to which is Ø22 mm. Because of this the pipe leading up to this point is also done with Ø22 mm. His suggestion was to increase this supply pipe but I'm not sure this will do any good. Rather the opposite...
Any thoughts on whether this will help and if no, what should be done?
 
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What changes were made between the two valves? Are they of different types?
 
The first thing I would make sure is that both valves have the same or close to equivalent Cv (or for you European folks, an equivalent Kv).
 
Increasing the size of the pipe supplying your valve assembly will help with the pressure at the valve, but... If the pressure was acceptable before, it may be easier to change out the valve than to change out the supply piping.

It also occurs to me that the new valve is flowing more - and that would increase the pressure drop along the supply piping. I'm not sure if that makes sense, I have to think about it for awhile.
 
minger said:
What changes were made between the two valves? Are they of different types?

I'm not sure, but I believe the old tap only had a 15 mm supply pipe so I suppose it probably delivered less water but with better "force" or pressure at the end. Does that make sense?
 
TSN79 said:
I'm not sure, but I believe the old tap only had a 15 mm supply pipe so I suppose it probably delivered less water but with better "force" or pressure at the end. Does that make sense?
Not really, no. What is on the end? If the nozzle, faucet, or whatever is on the end hasn't changed, the larger piping and valves leading to it provide lower resistance and therefore greater flow and pressure at the end.
 
russ_watters said:
Not really, no. What is on the end? If the nozzle, faucet, or whatever is on the end hasn't changed, the larger piping and valves leading to it provide lower resistance and therefore greater flow and pressure at the end.

The user probably connects a 3/4" hose to the nozzle. I'm just thinking that many just pinch the end of the hose in order to get more "pressure" out the end, so won't reducing the supply pipe do sort of the same thing...?
 
Well, if I understand this right, the new valve has a bigger diameter than the previous one. Is this correct? I also assume the water supply has not been changed?

Now, careful not to mix force and pressure! Force is due to the water supply, while pressure is the force divided by the area of the valve (ie A = pi*radius^2 and P=F/A)

If your customer wants greater PRESSURE from the valve, change the diameter of the valve. By mass conservation however, the water supply should not be affected by this, as the water coming in (from the water supply) must be equal to the water coming out of the valve, regardless of the diameter of the valve.
 
TSN79 said:
The user probably connects a 3/4" hose to the nozzle. I'm just thinking that many just pinch the end of the hose in order to get more "pressure" out the end, so won't reducing the supply pipe do sort of the same thing...?
Yes, at the pinch. Past the pinch, the pressure drops because the pipe gets bigger again as per Bernoulli's principle.

It is possible I'm misunderstanding what this looks like, though - perhaps you could upload a sketch...?
 
  • #10
AppleBite said:
If your customer wants greater PRESSURE from the valve, change the diameter of the valve.
I can't fathom an application where someone would want a higher pressure behind a valve via changing the valve size - all you are doing is adding loss to the system.
 

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