Description

Thermostatic Mixing Valve for Hot Water Temperature Control

The LK 551 HydroMix is a thermostatic mixing valve from LK Armatur, designed for water heating and heating systems where reliable and stable mixed-water temperature is required.

The valve uses a thermostatic element to automatically regulate the flow of hot and cold water and produce water at the desired outlet temperature. It also incorporates an anti-scald function, which shuts off the incoming hot-water flow if the cold-water supply fails.

This makes the LK 551 HydroMix particularly suitable for domestic hot-water systems, water-heating equipment and applications where protection against excessively hot water is important.

Key Features

• Thermostatic temperature control
• Anti-scald protection
• Adjustable outlet temperature
• Protective temperature-setting cover
• Compact design
• Brass valve body
• Female-threaded and male-threaded configurations
• Temperature stability of approximately ±3°C
• Maximum working pressure of 10 bar
• Suitable for water and specified glycol/ethanol mixtures

How the LK 551 HydroMix Works

The LK 551 HydroMix is an asymmetrical three-port thermic mixing valve.

The valve has three connections:

• C – Cold water inlet
• H – Hot water inlet
• M – Mixed water outlet

The thermostatic element continuously responds to the temperature of the mixed water and adjusts the proportion of hot and cold water entering the valve.

The operating principle can be represented as:

Hot Water (H)
↓
LK 551 HydroMix → Mixed Water (M)
↑
Cold Water (C)

If the mixed-water temperature becomes too low, the valve increases the hot-water contribution.

If the mixed-water temperature becomes too high, the valve reduces the hot-water contribution and increases the cold-water contribution.

Anti-Scald Protection

One of the most important features of the LK 551 HydroMix is its anti-scald function.

If the cold-water supply fails, the valve is designed to shut off the incoming hot-water flow.

This provides an additional level of protection against excessively hot water reaching the outlet.

The anti-scald function is particularly important in domestic hot-water applications where users may be exposed directly to the mixed water.

Adjustable Temperature

The LK 551 HydroMix is available with different thermostatic temperature ranges.

According to LK Armatur, the available operating ranges include:

• 10–30°C
• 25–45°C
• 35–55°C
• 35–65°C

depending on the specific valve configuration.

The temperature is adjusted using the valve knob.

A protective cover helps prevent accidental changes to the selected temperature setting.

Temperature Stability

LK Armatur specifies a temperature stability of approximately:

±3°C

This allows the valve to maintain a relatively stable mixed-water temperature under suitable operating conditions.

Actual temperature performance will depend on factors such as:

• Hot-water temperature
• Cold-water temperature
• Differential pressure
• Flow rate
• Valve size
• System configuration

Pressure and Temperature Ratings

The LK 551 HydroMix has a maximum working pressure of:

1.0 MPa (10 bar)

LK Armatur specifies working temperatures of:

• 5–65°C
• 5–95°C

depending on the relevant configuration/application.

The specific operating temperature range should therefore be checked against the selected article number and thermostatic element.

Valve Body Material

The valve body is manufactured from:

Brass EN 12165 CW617N

CW617N is a commonly used copper-alloy material for valves and plumbing components.

The brass construction provides a compact and corrosion-resistant solution for water-heating applications, subject to the actual water chemistry and service conditions.

Connection Types

LK 551 HydroMix is available with threaded connections.

LK specifies:

• Rp – female thread
• G – male thread

The current product range includes female-threaded variants such as:

• ½”
• ¾”
• 1″

with different Kvs values and temperature ranges.

Available Sizes and Kvs

The current LK Armatur product information lists the following female-thread variants:

These variants have different flow capacities and thermostatic temperature ranges, so the article number should be selected according to the required flow rate and outlet temperature.

Kvs and Flow Selection

The Kvs value indicates the valve’s flow capacity.

The available LK 551 HydroMix configurations have Kvs values ranging approximately from:

1.5 to 4.2 m³/h

depending on the selected variant.

When selecting the valve, the Kvs should be checked against the required flow rate and allowable pressure drop.

A simplified relationship is:

Higher required flow → Higher required Kvs

However, the final selection should be based on the manufacturer’s capacity diagram and actual system conditions rather than nominal pipe size alone.

Applications

The LK 551 HydroMix is primarily intended for water heating and heating systems.

Typical applications include:

Domestic Hot Water

The valve can mix hot and cold water to provide a controlled outlet temperature.

Water Heaters

The valve can be installed downstream of a water heater or storage tank to control the temperature delivered to the system.

Hot Water Storage Tanks

The thermostatic mixing function helps reduce the risk of excessively hot water being delivered to users.

Heating Systems

The valve can also be used in suitable heating applications where thermostatic mixing of hot and cold water is required.

LK Armatur specifically describes the LK 551 HydroMix as an asymmetrical mixing valve for water heating and heating systems.

Installation on Water Heaters

When the LK 551 HydroMix is installed on top of a boiler or storage tank with a built-in water heater, LK Armatur recommends leaving some space between the tank and the valve.

This is intended to prevent heat radiation from the tank from affecting the operation of the valve.

Correct installation is important because the valve’s thermostatic element must accurately sense the mixed-water temperature.

The flow-direction arrows on the valve body identify:

C = Cold Water
H = Hot Water
M = Mixed Water

No Routine Maintenance Required

LK Armatur states that the LK 551 HydroMix requires no maintenance, but recommends that the installation be checked regularly.

Regular inspection can help verify:

• Correct temperature
• No leakage
• Proper connections
• Correct flow direction
• Correct temperature-setting position

Accessories and Spare Parts

LK Armatur provides a range of accessories and replacement parts for the LK 551 HydroMix.

These include:

• Repair kits
• Connection kits
• Check valves
• Insulation
• Gaskets and associated components

For example, LK lists connection kits with rotating nuts, gaskets and one or two check valves, depending on the configuration.

This can simplify installation and future servicing.

LK 551 HydroMix for Hot Water Systems

A typical domestic hot-water arrangement can be represented as:

        HOT WATER
            │
            │
       ┌────▼────┐
       │         │
       │ LK 551  │──────► MIXED WATER
       │ HydroMix│
       │         │
       └────▲────┘
            │
            │
       COLD WATER

The thermostatic element automatically adjusts the ratio of hot and cold water to maintain the selected mixed-water temperature.

This eliminates the need for continuous manual adjustment.

Advantages of LK 551 HydroMix

1. Automatic Temperature Control

The thermostatic element automatically regulates the mixed-water temperature.

2. Anti-Scald Protection

The hot-water inlet is shut off if the cold-water supply fails, providing protection against excessively hot water.

3. Adjustable Temperature

Different thermostatic temperature ranges are available according to the application.

4. Compact Design

The valve is suitable for installation in relatively confined plumbing and heating systems.

5. Stable Temperature

LK specifies approximately ±3°C temperature stability.

6. Brass Construction

The valve body uses EN 12165 CW617N brass.

7. Spare Parts Availability

Repair kits and connection accessories are available from LK Armatur.

Technical Specifications

Specifications are based on LK Armatur’s current product information and catalogue.

LK 551 HydroMix vs. Conventional Manual Mixing Valve

The major advantage of the LK 551 HydroMix is that the operator does not need to continuously adjust the valve to compensate for changes in hot- or cold-water conditions.

Important Selection Considerations

When selecting an LK 551 HydroMix, consider:

• Required outlet temperature
• Required flow rate
• Kvs
• Hot-water temperature
• Cold-water temperature
• Differential pressure
• Connection size
• Working pressure
• Maximum working temperature
• Water quality
• Applicable local plumbing requirements

The valve should be selected according to the actual operating conditions rather than simply matching the pipe connection size.

Conclusion

The LK 551 HydroMix is a compact thermostatic mixing valve designed to provide stable and controlled mixed-water temperature in water-heating and heating systems.

Its combination of automatic thermostatic regulation, adjustable temperature, anti-scald protection, brass CW617N construction and ±3°C temperature stability makes it a practical solution for domestic hot-water and heating applications.

With available ½”, ¾” and 1″ configurations and Kvs values from approximately 1.5 to 4.2 m³/h, the LK 551 HydroMix can be selected for a range of small and medium water-heating applications.