Three-pass warm-water and hot-water boilers combusting gaseous and liquid fuels
In compliance with the requirements of standard ČSN EN 12 953 and directive EC 97/23

Design
The boiler body consists of a cylindrical shell, two reinforced bottoms, a symmetrically bedded boiler flue, a water cooled inflective chamber and a ring nest of stay tubes of the second and third pass. The front inflective chamber is not cooled. It is closed with a door enabling cleaning of the generating surfaces. Boiler venting is provided by a flue gas collector in the rear part of the boiler. Flue gas discharge is realized via a chimney neck with an upper or rear outlet.

Equipment
The boiler body is equipped with a relief valve and draining. The outlet and reverse necks are fitted with adaptors with lugs for installation of measurement and regulation instruments. Beneath the return water inlet neck there is an injector increasing the output temperature.
Hot-water boilers are additionally equipped with a pressure limiter. Warm-water boilers are additionally equipped with a temperature limiter, namely up to 110°C.
Manholes together with inspection holes enable inner revision of the boiler.

Efficiency
The heat contained in flue gasses leaving the boiler can be transferred to return water in the exhaust-heat exchanger. Energy gained this way increases the boiler efficiency of up to 7% reducing thus the fuel consumption.

Economizer
It supplements the basic design of the PB-V and PB-H boilers. It can be integrated into the flue gas collector or autonomously placed at the flue gas outlet.
The economizer provides a highly efficient heat transfer - the counter-flow principle. It consists of nests of finned or plain tubes in the flue gas channel with admission in the water chambers.

Flue gas exchanger connection
With regard to the boiler output and the design efficiency two basic types of the exchanger connection are distinguished.
Version with a full flow - all the return water flows through the exchanger, where it is preheated.

Version with a partial flow - only a part of the return water (10 - 30%) flows through the exchanger. Before the boiler inlet the rest of the return water mixes with heated water from the exchanger. This version is mainly used for boilers with a higher flow rate of recirculation water.

Modifications
The design of the boilers enables using an identical construction for both warm-water and hot-water boilers, namely up to pressure of 16 bars.