Valve

Theme Valve : The black opens a line for one of his pieces, closing another line of the same piece.

	(Problem 71) C. S. Kipping, First Prize, ”S. Glasnik”, 1947 White plays and mates in 3 moves #3 (8+11)
[rb4br/2p2p2/1p4p1/2p1P3/1p2BQ2/4PS2/4SKP1/3k4]

In problem-71, by Kipping, we see two valves.
Tries: {1.Qh2? Rxh2!}, {1.Qf5? gxf5!}, {1.Qg4? f5!}, {1.Bc2+? Kxc2!}.
Key: 1.Qf6! [2.Qd8#]
1...Bh7 2.Qh4 [3.Qh1#] Bg8 3.Qd8#
1...Ba7 2.e6 [3.Qa1#] Bb8 3.Qd8#


In the next Problem-72, by Matthews, the Bishop opens a Rook line, but closes another Rook line, (with the Rook staying on its square, or moving to a better defensive position).

	(Problem 72) R. C. O. Matthews, ”The Problemist”, 1950 White plays and mates in 3 moves #3 (10+11)
[r4b2/6p1/1p6/3B1pP1/4pP1B/2P1pS1p/2PSK1kp/4R2b]

Tries: {1.Bf2? exf2!}, {1.Kxe3? Bc5+!}, {1.Sf1? / Sc4? Bc5!}, {1.Rxh1? Kxh1!}, {1.Rf1? Ra1!}.
Key: 1.Sxe4! [2.Bf2 [3.Sh4#]].
The pair of the Knights has formed a half-battery with the Bishop so, if one of the Knights is lifted and then the other is lifted, a check from Bd5 is discovered.
It is not good to play 1...fxe4 2.Bxe4 Ra4 / Re8 3.Sd4# / Se5#
If the Bishop Bf8 is lifted, then the Rook Ra8 will be able to run to h8 to void the threat of the key. But the black Bishop can not stay on the air, but must come down on some square... Let us see five variations.

(a) 1...Be7 2.Sd4
(The plan is to lift also Se4 and Bd5 to check Kg2. The Rook Ra8 can not interfere in the diagonal d5 – g2 reaching e4, because the row is closed by the Sd4 and the file is closed by Be7. So the Rook will attack Bd5).
2...Ra5 / Rd8 3.Sc5# / Sd6#

(b) 1...Bd6 2.Sc5
(The plan is to lift also Sf3 and Bd5 to check Kg2. The Rook Ra8 can not attack Bd5, because the row is closed by Sc5 and the file is closed by Bd6. So the Rook will interfere in the diagonal d5 – g2 reaching e4).
2...Ra4 / Re8 3.Sd4# / Se5#

(c) 1...Bc5 2.Sd6
(The continuation is exactly the same as in variation-b).

(d) 1...Bb4 2.Se5
(The continuation is exactly the same as in variation-a).

(e) 1...Ba3 2.Rf1 and 3.Se1#
(Because Ra8 can not reach a1).

[This post in Greek language].