Showers – Pressure Balance Valves Explained

Palladium PB Valve by Rohl

There are probably three main factors that will influence shower performance; waterpressure, shower head and the shower valve. In this post I am going to discuss pressure balancing shower valves. The code today requires shower valves to be anti-scald and pressure balance is one type of anti-scald valve.


 A pressure balancing valve accomplishes the anti-scald function through either a balancing spool or a diaphragm system. Both work by responding to a sudden drop in pressure in the incoming water, usually on the cold side. In a spool system the balancing spool may be either within the cartridge or in a separate spool cartridge. If the pressure of water coming in on the cold side suddenly drops it will cause the spool to shift and reduce the incoming hot water thus balancing the pressure (and the temperature). A diaphragm system has a centered diaphragm with the hot/cold inlets on either side. If the incoming pressure drops on one side the diaphragm moves to

Grohe 35015 Pressure Balance Valve Rough - Cycling, Diaphragm

reduce the incoming water on the other side.

 Both systems produce similar results however a diaphragm system is typically more trouble free. This is because a spool system can become stuck if there is a build up of sediment. This will cause the balancing spool, and the valve, to stop working. It is then necessary to remove the spool and clean it or replace it. A diaphragm system is not as vulnerable to the sediment build up and tends to remain trouble free much longer. Better quality valves may include filter screens which prevent the sediment from damaging the valve.


 Another feature to look for is whether the valve is a “cycling” or “non-cycling” type. In a cycling valve the handle turns counter-clockwise with the temperature moving from cold to hot. You stop turning when you reach the temperature you want. A cycling valve is either on or off, with no adjustment of the volume available. A non-cycling valve gives the user control of both the volume and temperature.

Rohl R2012C - Top of the Line Non-cycling, Diaphragm

Another point to consider is the range of temperature control available. Imagine a clock. In some valves the temperature range from coldest to hottest happens from 6 o’clock to 3 o’clock (90 degrees) while in others it may be to 12 o’clock or even 9 o’clock (180 to 270 degrees). Why is this important? Because with the short range valves a very small movement of the handle may result in a big change in temperature. If you have ever used a shower where you seem to get only too hot or too cold you know how annoying this is. It is a detail that is often missed but is certainly important when you are using the shower.


Another consideration is flow rate. Flow rates can vary from approximately 4.5 gallons per minute to 9 gallons per minute depending on the valve. If you have just a single shower head then any of these will deliver enough water but if you are filling a tub (especially a large one) or have a second shower head you may want to check carefully on the flow available with the valve you select. I have found 4.5 – 6gpm to be the norm although some manufacturers, for example Rohl and Kohler do offer high flow valves that can deliver as much as 9 gpm.

Metris C Pressure Balance by Hansgrohe


 Valve trim usually looks good when you see a picture or a display in the showroom. The real test of its quality however is how in performs once installed and after it has been used for a few years. That is when you will really start to see the quality (or lack of). You want handles that fit well without a lot of play and trim plates that are well finished. It is often true that more economically prices trim may include plates or handles made of plastic or zinc alloy (even though the finish is chrome or another metal look). This is not always bad but is something to be aware of.

 Use these guidelines and you will be on your way to building a shower you can enjoy for years.

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