From: "stephen wozniak" <stevewozniak42@hotmail.com>
To: technical@sunvic.co.uk
CC: sales@sunvic.co.uk
Subject: failure of two-port valve actuators
Date: Mon, 29 Jan 2007 18:13:03 +0000 (date and time when originally sent)

David Wigam
Sales & Marketing Director
Sunvic Controls Limited
Bellshill Road
Uddingston
Glasgow
G71 6NP

sales@sunvic.co.uk
technical@sunvic.co.uk

Failure of 2 port MoMo valve actuators type SZM 1801, purchased October 2003.

Quote: "Sunvic Controls Ltd has launched a brilliantly innovative, totally reliable range of two and three-port motorised valves for domestic central heating."

Quote: "These patented MoMo motor-open/motor-off valves, available as two-port or three-port in all popular sizes, provide total reliability plus compatibility with existing and conventional wiring systems."

To begin, I cannot find the type number SZM 1801 on your website but the actuator bodies have a label attached bearing Patent Pending GB0222324.6 which aligns with Patent GB2393490 on the Patent Office website - so I am assuming you did make the actuators in question.

I am experienced in design and installation of central heating having been a research scientist in H&V for many years. I have also personally installed probably a dozen of your earlier type MINIVAL SM 3203 actuators. A couple of these are still working perfectly in my own home after 10 years. I am familiar with the problems of the earlier type spring-return valves that led directly to your marketing of 4-wire compatible MoMo designs.

On 6 October 2003 I purchased from B&Q in Exeter two complete two port valve assemblies that incorporated SZM 1801 actuators. Both of these failed recently and in an identical fashion.

The valves were purchased as part of an upgrade package - comprised the usual room stat, cylinder stat, two 2-port valves etc and was undertaken with a view to making later installation of a more modern boiler much easier. As you will be aware, these require a fully pumped system.

Failure of the valve used on the CH was first noticed in December 2006 (although when it first exhibited erratic behaviour is uncertain) and the DHW valve failed [later]

I have now turned my attention to exactly what is wrong with these valve actuators. On test, both always switch off reliably and are 'stable' in the off position. It is switch-on that is the problem. When power is applied to the brown wire, sometimes the valve motor will run but more usually not - except that is when the assembly is subjected to vibration or a sharp tap on the outer casing. This mechanical disturbance is always sufficient to 'wake up' the motor and gear mechanism - which then operates perfectly.

The intermittent operation is thus explained - vibration from the nearby pump and the odd bit of creaking pipework could have been quite sufficient to 'nudge' a valve into operation. Indeed, it is possible that the vibration from the DHW valve turning off under time-switch or cylinder stat control (for example) would have been sufficient to nudge the closely adjacent CH valve to operate if it had been electrically commanded to switch on but had failed to respond.

Once the actuators are switched on and 'open' no amount of vibration or tapping will cause them to switch off. The only other significant observation is that the actuators seem to exhibit worse behaviour when 'horizontal' than when 'vertical' (that is, how they would be if installed in vertical pipework). Gently lifting a non-responding valve from the horizontal to vertical position (with the motor shaft now horizontal) can be sufficient to cause it to operate. In situ, the valves were in vertical pipework, which may explain why their failure was not noticed sooner.

Other curious behaviour includes that when the valves are 'open' and power is removed (to mimic a power cut), sometimes but not always both valves will undergo a complete cycle when power is restored, but with one or other valve (sometimes both of them) failing to return to the 'on' or 'open' position. It is then necessary once again to tap the casing(s) to initiate rotation to the open position.

Before I delve further into exactly why these valves are behaving in this curious manner I would like to know if you recognise a generic design or quality problem with valves of this vintage. It is probably either a simple matter of poor design of the microswitch operating 'lugs' which makes them susceptible to a very slight amount of wear - or maybe the hysteresis in the microswitches themselves or the considerable amount of 'free movement' in the gearing has not been adequately accommodated. The other possibility is that the relay contacts have 'burnt' or become high resistance. I note from your Patent for these valves the following text that describes the operating sequence for opening a valve:

"As with a conventional spring-return valve, the control electronics, as 5 shown in Fig. 4, has four input wires coloured brown, blue, orange and grey. As with a spring-return valve, there is one wire (the brown wire) that controls both opening and closing of the motorised valve. When mains power applied to the brown wire, this is a signal to open the valve. When this power is removed, the control circuitry provides the 10 required signal to the motor drive 10 to close the valve.

As shown in Fig 4, the brown input is reduced in voltage and rectified by a series capacitor C1, a bridge rectifier BR1 and a parallel capacitor C2.

The blue wire provides a return path for the AC input. This provides a low voltage DC signal for operation of a relay RL1. When power is 15 applied to the brown wire, the relay RL1 operates and is held closed to cause mains applied to the grey wire to be transferred to a first of the microswitches, labelled S1 in Fig 4. The microswitch S1 transfers power from the grey wire to the motor drive 10, causing it to start rotating.

This, in turn, drives the connecting member 30 and the valve spindle in 20 the forward direction, once all lost motion has been taken up.

Movement continues until the button of the microswitch S1 enters the corresponding cam slot 34. This turns the microswitch S1 off, and the motor drive stops. At this time, the valve is in the open condition."

It would seem that failure of relay RL1 to operate (maybe because it is a low-spec design and the contacts have 'burnt' after only a few years' operation??) would indeed cause all the symptoms that have been experienced. From the evidence so far available, this seems to me to be the most likely explanation. The entire central heating system is fused at 3 amp as per boiler manufacturers recommendations - and your actuators should easily be able to accommodate this loading. The correct performance of these does of course depend crucially on proper long term reliability of RL1.

I am particularly disappointed in all of this because I deliberately chose 2 two-port motor-on motor-off valves because I had always found these to be more reliable than the more usually installed three port designs - to say nothing of spring return two-port types.

The date codes on the motors are 03-03 and 49-02 but this is hardly relevant as there appears to be nothing wrong with the actual motors.

The date codes on the undersides of the actuator bodies are 04-03 and 06-03, all of which is consistent with purchase in October 2003. I have the original receipt.

I await hearing from someone competent in your technical department.

In the meantime I will continue to investigate whether any other feedback from users or further relevant information is available on the Internet.

Yours sincerely

Dr Stephen J Wozniak
29 January 2007