The Steam turbine combined trip and throttle valve was received in a very poor condition and appeared to have not been used for some considerable time.
Trip and throttle valves are integral to the safety and precisely control the speed / load of the steam turbine, typically drive an alternator, pump or fan.
Steam valves generally get very rusty, due to the nature of the harsh environment, as you can see from the before photograph.
Sequence of overhaul;
The first step we take when performing an overhaul on any valve is to photograph its initial state and also as we gradually strip the valve, more photos are taken.
The valve is then dismantled and cleaned by paint stripping and bead blasting to remove all rust and dirt, then chemically cleaned.
Once all parts are clean, they are then laid out and inspected for wear, damage and corrosion. Only then our technicians will ascertain what will need replacing.
A Standard overhaul kit was fitted, in addition to valve stems, pins, main studs, washers, adjusting screws, main gaskets used plus machining on some major parts carried out.
The valve was then meticulously re-built and mechanically tested to ensure the unit was back to original specification.
The finished valve was dispatched in a bespoke wooden packing case and delivered safely back to the customer by our own EGS transport.
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We have just completed another successful overhaul job of 4 large steam valve actuators and Voith Way Valves for steam turbines situated in a recycling plant. This particular plant recycles domestic waste into electrical energy, which subsequently exports to the National Grid.
This job was interesting for our engineers, as all 4 actuators were received in a stripped and broken down state, as the plant engineers had tried to examine the actuators themselves and in turn had severely damaged vital components on the 4 units.
After all components were chemically cleaned and stripped of any paint, they were then fully inspected to see the extent of the destruction. Major components were replaced as well as ‘O’ rings, piston rings, seals, receptacles and all consumable fasteners renewed.
Our machine shop carried out bore honing to suit over sized pistons. Grinding and re-chroming piston stems to standard size. We also manufactured piston bearing/ seal housings.
Each steam valve actuator uses a Voith Way Valve, so these were also overhauled. The ‘Way Valve’ controls the hydraulic pressure, monitoring the feedback (LVDT) positioning sensor for each valve when fitted to the steam turbine.
Once all units were carefully re-assembled and painted a vibrant blue colour, they then had to be tested. Our Applications Engineer has built customised test equipment to aid in the examination of the output figures that each complete actuator should read. The Voith over speed trips were tested to factory settings. Each unit took approximately 2 hours to gain full accurate readings.
On completion of test, all equipment was delivered to site by our EGS Engineers, who were on hand to assist with installation.
With a lot of careful planning and production meetings, EGS were able to complete and turnaround this job in 4 weeks.
We received a UG8 Governor clearly showing signs that it had undergone a bad and cheaply done overhaul – this was a prime example of how a governor should not be overhauled!
- Once this particular governor was stripped down it was clear that the parts had been shot blasted, which included parts made to fine tolerance e.g. pilot valve and bushing. Some internal parts are coated and by using harsh blasting methods the coatings / layers will be removed and service life will be considerably reduced. We carry out vapour blasting on castings and non fine tolerance items, this is a gentler and finer process that does not cause damage to parts. The parts are then thoroughly cleaned and inspected for wear / damage.
2. It was evident that this governor had not been updated with the latest specification of parts but instead the old parts had merely been cleaned and re-assembled. Once our inspection has taken place ALL worn / corroded / damaged parts are replaced with NEW and updated spares.
- It was obvious that some castings showed clear signs of rust and pitting. There was no protective coatings on any of these parts, it was easy to tell that some of the castings had not been renewed as they should have been. We ensure that our supplied castings have a protective layer on the metal as this protects parts from harsh conditions causing slower wear, meaning a longer life in service.
As this governor was in such a bad state it was deemed uneconomical to repair, so our customer opted for a reconditioned unit.