Two-stage cyclone filtration system for T-80U

 The deployment of BMP-1, BMP-2 IFVs, T-64A, T-64B and T-80 tanks with single-stage air filtration systems with an average purification rate of 99.8% confirmed their superiority over existing two-stage filter systems: lower weight, smaller dimensions and easier maintenance. 

While the given purification rate of 99.7-99,8%, achieved by the T-80's cyclone filter array, is substantial, it does not meet industry standards set by OST V 3-2627-75. 

OST V V-2627-75 is a Soviet and post-Soviet industry standard that dictates that AFV air filtration systems with cyclones have to meet necessary protection requirements against foreign debris that can get logged inside the cyclone cones, like pine needles, hay, dirt/mud, petroleum-based products, spent gas molecules, snow and others. This implies that the cyclones have to be protected by a mesh and or filter and can not be directly exposed to the environment.  

A blocked cyclone array can severely reduce the air supplied to the engine, resulting in an increased hydraulic resistance in the dust collector pan. A reduction of such operability lowers the rate at which dust is forcefully ejected out through an ejector duct into the exhaust. The worst-case scenario is that contaminated air is sucked back inwards, directly into the engine. 

Proposed implementations were developed and deployed using the T-80Us single-stage cyclone filter array. 

The following two goals were set: 

1.  Protection of the single-stage cyclone filter array, with the ability to perform diagnostics and retain the ability for the vehicle to ford bodies of water. 
2. Creation of a two-stage cyclone filter array that fits inside the T-80U engine-transmission bay. 

A more comprehensive comparison of the engine air filtration systems used at the time would be the two-stage cyclone filter system on the T-72. The main difference between the two is that the T-72B uses 3 filter cassettes after passing the air through the cyclones. In addition, the airflow of the T-72s air filtration system is the reverse of that on the T-80s. While the T-80 filtration system draws air from the environment down through the cyclones, the T-72s design ingests air through the bottom of the filtration unit using upwards pressure, passes the air through cyclones and up through the 3 screen meshes. 

T-72B air filtration system diagram 

 

T-80 air filtration system diagram

The aforementioned proposed design idea of implementing filter meshes within the cyclone array would require rebuilding the entire module, since the T-80s filter array is 1.9x smaller than the one used on T-72s. Such a redesigned implementation would make it difficult to retain the performance metrics without changing the engine-transmission bay layout. 

One of the proposed designs utilised 30mm x 150mm cyclones that could achieve an air-purification ratio of 99,4-99,5% and a hydraulic pressure resistance of 4,5-5,0 kPa, using 3 metallic filter cassettes of varying density: 0,4; 0,8; 0,95-1,0 g/cm^3. This combination could achieve an air-purification rate of 99,8% with pressure resistance at about 11,5 kPa. 

It is important to point out that the standard cyclones used on T-80s are 90mm in diameter.

Stationary tests showed that such an array filtering a contamination ratio of 2,0g/kg of air would require regular maintenance every 15 to 20 hours. The aforementioned is claimed to have been installed on 3 T-80U tanks and trialled in Central Asia with an average maintenance cycle of 3 to 4 hours. 

It was determined that cyclones with a diameter of 30mm offered optimal purification ratios of 99,85% with hydraulic pressure resistance of 10 kPa. It is theorised that if the purification rate is lowered by 0.05%, the pressure resistance can be lowered to 7,5-8,0 kPa. Stationary tests provided for the assumed performance metrics of a median 7,7 kPa of resistance and a purification rating of 99,8%. 

This partially concludes that a two-stage cyclone filter array with 30mm diameter cyclones and a 2-layer mesh filter cassette layout (0,8 and 0,95-1,0 g/cm^3 density) would provide near identical purification performance as the standard T-80 cyclone filter array, but with improved reliability that is found on two-stage filters. 

Unfortunately, there are no drawings or schematics of this finalised filter designed, but based on the description provided by Vestnik, the rough layout would resemble a similar design as seen on the original cyclone array, but with a 2-layer mesh array after the cyclones and in front of the central air duct.

Additionally, this designed and tested filtration system partially defeats the purpose of an engine that is already expensive and complicated to maintain. An observational point of view would find it difficult to understand a system that already functions within anticipated parameters when it is subjected to more servicing hours and complexity. The inbuilt systems that prevent the 0.3% of entering contaminants from clogging vital engine components are there to prevent this from happening. This idea is reasonable if the goal is to extend engine operating hours beyond what they are nominal, but as indicated by Vestnik, it requires alterations to the engine-transmission bay and possibly reworking of the monobloc. Near 100% purification rate would essentially remove the need to frequently use the pneumatic cleaning system used within the turbine. 

Lastly, the provided numbers of air purification rates vary quite a lot. Various sources that I have used previously state that the GTD cyclones offer 97%+ purification rate, while Vestnik, for example, offers nearly 100% purification ratios as seen in the discussed text. But these numbers should not be taken at face value, but do offer a small insight into the numeric perspective of such systems. 

Taken from: 

1. Вестник бронетанковой техники, № 3, 1989 - Новый малогабаритный 2-ступенчатый воздухоочиститель 
2. Основной танк Т-80. Безмолвное возмездие / Иван Павлов, Михаил Павлов. — Москва : Эксмо: Яуза, 2017
3. Плакаты Т-72Б