# Is pressure loss a good thing ?

• TSN79
In summary, the amount of pressure loss in a water based heating system can vary depending on the type of control and the desired outcome. In some cases, such as two position or modulating temperature control, a low pressure drop is preferred. However, for proportional control, a higher pressure drop is necessary for accurate control. It is important to consider the specific needs of the system when determining the appropriate pressure loss.
TSN79
In a normal water based heating system (boiler, radiators etc) I'm told that having a high pressure-loss over the radiator valves is a good thing? I'm just having trouble seeing why, since I always considered pressure-loss as the enemy (head-loss etc). Why is this good?

Also, I hear that there should be a certain amount of loss over balancing valves? Supposedly because it eases measuring?

You are correct: without a pressure drop, there is nothing to measure (or adjust) when you are balancing.

We're doing a project right now where my boss accidentally selected the wrong size circuit setter (a 3" instead of a 2") and when I tried to balance the flow through it, our hydronic manometer could not give steady readings because the pressure drop was too low.

Depends on what you are doing.

Two position (open and closed) water or steam, a low pressure drop is desired. Only require a drop of 10% of available pressure.

Modulating temperature control, such as Outdoor Reset, using a 3-way valve, the drop wants to be low, maybe 20% of available pressure.

Proportional control through a radiator or coil, the pressure drop wants to be higher, as you said. Industry standard is 3, 4, or 5 psi drop across a water control valve in a hydronic system. Or it can be equal to the pressure drop across the coil being controlled.

Proportional control in a 15 psi steam system requires 80% pressure drop for good control.

So, low pressure drop if you want to redirect or just stop the water flow (two position and modulating 3-way).

Higher pressure drop required if you need to just reduce or change the amount of flow (proportional control).

## 1. What is pressure loss and why does it occur?

Pressure loss is the decrease in force per unit area exerted by a fluid or gas as it flows through a system. It occurs due to friction, turbulence, or changes in direction of the flow.

## 2. Is pressure loss always a bad thing?

No, pressure loss can sometimes be beneficial. For example, in a hydraulic system, pressure loss can help to dissipate excess energy and prevent damage to the system.

## 3. How can pressure loss be measured?

Pressure loss can be measured using a pressure gauge or a manometer. These devices measure the difference in pressure between two points in a system.

## 4. What causes excessive pressure loss?

Excessive pressure loss can be caused by factors such as obstructions in the flow path, inadequate pipe size, or sharp bends in the pipes. It can also be caused by high viscosity fluids or high flow rates.

## 5. How can pressure loss be reduced or prevented?

Pressure loss can be reduced by using larger pipes, minimizing obstructions, and smoothing out sharp bends in the flow path. Regular maintenance and cleaning of the system can also prevent excessive pressure loss.

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